Version:           unknown (using KDE 3.1.93 (CVS >= 20031111), yes)
Compiler:          gcc version 3.2
OS:          Linux (i686) release 2.4.21-1up.1

Currently, a freshly started Konqueror cannot open a second tab (Location -> New Tab is disabled) before some viewer part loads something in the current window.

If you disable the Konqueror introduction in the web browsing view profile using config:/disable_overview, then Konqueror starts up with no part loaded (not even about:blank).

The combination of these two features means that you cannot open multiple tabs in a freshly started Konqueror window.  This might almost be OK, except that some actions (e.g., fetching a web page) do not display anything until some of the content arrives.  So, if you open a slow-loading web page first, then you cannot open a second tab and do something else while you're waiting for the first tab to load.

This limitation is also inconsistent with two other Konqueror behaviors:
+ You can always open a new window.  "Open new tab" should be enabled whenever "open new window" is enabled.
+ If you already have multiple tabs, and the current tab is empty, then you can open a new window.  (This may be because empty tabs are created with about:blank instead of nothing.)