This happens 1-2 times a day for me. After closing a window - the taskbar will be all funny. Two taskbar entries are tangled into each other - and the first taskbar entry is empty without the rest of the taskbar entries falling in to the left. The only way to change this seems to be to open a new window - e.g. dolphin or kate. This has happened for me for at least 2 years and with different computers and different profiles (although all Kubuntu). Reproducible: Sometimes
Created attachment 79758 [details] Empty spot in taskbar dragged to dolphin. Today I was able to drag from the empty spot on the taskbar into a dolphin window - hoping that it would give some hint of what is causing the trouble. See the data attached. the CLI "file" tool returns that it is a "VMS Alpha executable". I don't know if that is a false positive.
Now I have 80% reproduceability on a guest account on my computer. And video showing it. For some reason It works best if windows are maximized. 1) close all windows 2) Open dolphin via k-menu 3) Open another dolphin via k-menu 4) Open Libreoffice Writer 5) click dolphin1 in taskbar 6) click dolphin2 in taskbar 7) right-click libreoffice writer in taskbar and click close. result: the first taskbar entry becomes empty. Video 1: Empty slot in taskbar efter closing window: https://dl.dropboxusercontent.com/u/22090107/20130603_115001.mp4 Video 2: taskbar entries tangling after closing window: https://dl.dropboxusercontent.com/u/22090107/20130603_113811.mp4
*** This bug has been marked as a duplicate of bug 226355 ***