Comment 22 for bug 335730

It is still here in Karmic, and it is easy to reproduce. With maximized, not decorated window you need to open dialog from any panel applet. E.g. bluetooth-applet -> send files to device or user-switcher -> Edit Personal Information. Then close the dialog and panel will disappear.
To get panel back again I use power button which brings shutdown dialog. Sometimes I need to press it twice. Shutdown dialog will appear and panel will appear too.