And there is one more really annoying and unreproducable issue.

I use the windows-quicklaunch in all themes and usually deactivate the quicklaunch-bar that comes with the theme.

Sometimes it happens that the icons/menu-items in the quicklaunch-menu disappear. The menu itself is still there, just the contents are gone. No theme-switching will help, nor does killing and restarting the core.

The quicklaunch is just empty and stays empty until the next reboot or logoff/logon.

This happens randomly and without any reason that I can identify, but it happens quite often, sometimes even in sessions where I don't switch themes or modify anything else in LS.