Created attachment 64496 [details]
Taskbar with a lot of empty rectangles.

Version:           unspecified (using Devel) 
OS:                Linux

I am using KDE 4.7.2 from openSUSE packages.

I've simple taksmanager widget on my only panel, that is configured as follows:

- force row settings - checked
- show tooltips - checked
- highlight windows - checked
- maximum rows - 1
- grouping - do not group
- sorting - alphabetically
- only show tasks from current screen - checked
- only show tasks from current desktop - checked
- only show tasks from current activity - checked
- only show tasks that are minimized - unchecked

I'm using only one activity (only one is configured).
I'm using 9 virtual desktops in 3x3 grid.
I'm using Akregator on my 3rd desktop (it is forced on 3rd desktop by Kwin special application setting).

My focus stealing-prevention policy is set to "medium" and focus is "click to focus".

After using one VD and switching to another using systray - taskbar on original desktop gets broken.

Reproducible: Always

Steps to Reproduce:
1. set up akregator to display tray icon, make this tray icon always visible
2. set up at least 2 virtal desktops
3. force akregator on second virtual desktop
4. run akregator
5. make sure at least one taskmanager widget is available on current setting and is is configured as in bug details
6. switch to 1st virutal desktop
7. open 5 konsole instances
8. click on akregator systray icon, you should be moved to 2nd VD
9. click on akregator systray icon, akregator should get hidden
10. switch to 1st virtual desktop, taskbar should have one empty rectangle at begining
11. repeat 8-9-10 to make this effect more visible

Actual Results:  
Taskbar have one empty places.

Expected Results:  
Taskbar does not have one empty places.