A malicious client may be eavesdropping on your session
or you may have just clicked a menu
or some application just decided to get focus.
I'm, using LM6 = all I'm doing is clicking on an application in mintmenu.
the mintmenu doesn,t disappear ( quick enough ) to make way for the application that is starting.
Please edit your original post title
to include [SOLVED] - when your problem is solved!