Version:            (using KDE 4.3.4)
Installed from:    openSUSE RPMs

Often, for no apparent reason, duplicate entries for a running application show up in the taskbar.  I'm not sure what causes this; it might have something to do with making the window sticky across all desktops.

Anyway, once a duplicate entry occurs, it doesn't function the same way a normal taskbar entry does.  For example, see the attached video, where KDE has created zombie taskbar entries for kopete and ktorrent.  At the beginning of the video, ktorrent is minimized to the system tray.  Clicking on the zombie taskbar entry has no effect.  I then restore ktorrent by clicking on its system tray icon.  The real taskbar entry appears, resulting in two taskbar entries for ktorrent.  Now the left ktorrent taskbar entry can be used to restore or minimize ktorrent, whereas the right entry has no effect.

At the end of the video I quit ktorrent.  One of the taskbar entries disappears, but a zombie one remains.  Clicking on it has no effect.  It just sits in the taskbar forever.

I've observed this behaviour with ktorrent, kopete, kontact, and other applications.