Version:           3.5.3 (using KDE KDE 3.5.5)
Installed from:    Debian testing/unstable Packages
OS:                Linux

Given identical HTML and identical CSS, except for the difference that one uses the MENU tag and the other uses the UL tag, Konqueror will render the one that uses MENU in a very inconsistent way.                                                                                               
                                                                                                                                   
The following HTML snippet illustrates the problem:                                                                                 
                                                                                                                                    
----------- cut here -------------- 8< -----------------------------                                                                
<style type="text/css">                                                                                                             
                                                                                                                                    
html, body {                                                                                                                        
   color: black;                                                                                                                    
   background-color: white;                                                                                                         
}                                                                                                                                   
                                                                                                                                    
/* All links */                                                                                                                     
#topnav a {                                                                                                                         
   text-decoration: none;                                                                                                           
   color: inherit;                                                                                                                  
   padding-left: 0.5em;                                                                                                             
   padding-right: 0.5em;
}                                                                                                                                   
#topnav a:hover {                                                                                                                   
   color: white;                                                                                                                    
   background-color: black;                                                                                                         
}                                                                                                                                   
#topnav ul {                                                                                                                        
   list-style: none;                                                                                                                
}                                                                                                                                   
                                                                                                                                    
/* Main horizontal menu */                                                                                                          
#topnav ul li {                                                                                                                     
   float: left;                                                                                                                     
}                                                                                                                                   
                                                                                                                                    
/* Submenus */                                                                                                                      
#topnav li > ul {                                                                                                                   
   display: none;                                                                                                                   
}                                                                                                                                   
#topnav li:hover > ul {                                                                                                             
   display: block;                                                                                                                  
}                                                                                                                                   
#topnav li ul {                                                                                                                     
   position: absolute;                                                                                                              
   float: none;                                                                                                                     
   padding-left: 0;
   border: 2px solid black;                                                                                                         
}                                                                                                                                   
#topnav li ul li {                                                                                                                  
   display: block;                                                                                                                  
   position: relative;                                                                                                              
   float: none;                                                                                                                     
}                                                                                                                                   
#topnav li ul li a {                                                                                                                
   display: block;                                                                                                                  
}                                                                                                                                   
                                                                                                                                    
</style>                                                                                                                            
                                                                                                                                    
<div id=topnav>                                                                                                                     
<ul>                                                                                                                                
<li><a href="#">File</a>                                                                                                            
    <ul>                                                                                                                            
    <li><a href="#">New</a>                                                                                                         
    <li><a href="#">Open</a>                                                                                                        
    <li><a href="#">Close</a>                                                                                                       
    <li><a href="#">Save</a>                                                                                                        
    <li><a href="#">Quit</a>                                                                                                        
    </ul>                                                                                                                           
<li><a href="#">Edit</a>                                                                                                            
    <ul>
    <li><a href="#">Undo</a>                                                                                                        
    <li><a href="#">Cut</a>                                                                                                         
    <li><a href="#">Copy</a>                                                                                                        
    <li><a href="#">Paste</a>                                                                                                       
    </ul>                                                                                                                           
<li><a href="#">View</a>                                                                                                            
<li><a href="#">Help</a>                                                                                                            
</ul>                                                                                                                               
</div>                                                                                                                              
----------- cut here -------------- 8< -----------------------------                                                                
                                                                                                                                    
This will generate a screen that looks like a normal GUI with File,                                                                 
Edit, View and Help menus. If the user hovers the cursor over File                                                                  
or Edit, a submenu is displayed; i.e., the screen looks like this:                                                                  
                                                                                                                                    
      File Edit View Help                                                                                                           
                                                                                                                                    
and, when hovered over File,                                                                                                        
                                                                                                                                    
      File Edit View Help                                                                                                           
      New                                                                                                                           
      Open                                                                                                                          
      Close                                                                                                                         
      Save                                                                                                                          
      Quit
                                                                                                                                    
and, when hovered over Edit,                                                                                                        
                                                                                                                                    
      File Edit View Help                                                                                                           
           Undo                                                                                                                     
           Cut                                                                                                                      
           Copy                                                                                                                     
           Paste                                                                                                                    
                                                                                                                                    
This is also the way Mozilla displays the HTML.                                                                                     
                                                                                                                                    
If the "ul" tags are replaced with "menu" tags, the screen will                                                                     
look completely garbled like this:                                                                                                  
                                                                                                                                    
      File New Open Close Save Quit * Edit                                                                                          
   * View                                                                                                                           
   * Help                                                                                                                           
                                                                                                                                    
The visible differences between this and how Konqueror renders the                                                                  
"ul" version are:                                                                                                                   
                                                                                                                                    
- The first submenu are interspersed between File and Edit                                                                          
                                                                                                                                    
- Unexpected bullets and alignment for the last 3 items                                                                             

The inconsistencies seem to be caused by Konqueror being confused                                                                   
by nested MENU elements, as can be seen from the following symptoms:                                                                
                                                                                                                                    
- The text contained inside the LI elements inside the nested MENU                                                                  
  are displayed as if they were part of the outermost MENU                                                                          
                                                                                                                                    
- The close tag of the nested MENU caused Konqueror to think that                                                                   
  the outermost MENU has closed                                                                                                     
                                                                                                                                    
- Subsequent LI elements seem to have caused Konqueror to insert                                                                    
  an implicit UL, thus causing the styling for MENU (specifically                                                                   
  the list-style and float properties) to be not applied                                                                            
                                                                                                                                    
- The Edit MENU is nested within the implicit UL (if UL is indeed                                                                   
  the implicitly-inserted tag), and Konqueror is thus not confused                                                                  
  by the nesting, and displays the submenu as expected                                                                              
                                                                                                                                    
The behaviour of MENU should be identical to UL. So nested MENU's                                                                   
are definitely allowed.

---
Note for Debian people: MENU is a valid element in 4.01, and the test case is rendered correctly by both Firefox and Safari.