Grey dialog boxes left around in Cinnamon

[Markus Lindholm]

I have a machine on which I did a fresh installation of F18 right
after it was released, now perhaps since a week I have this problem
that different application leave behind grey dialog boxes that sit on
the top of the desktop. For example every time I use Remmina to
connect to a remote machine it leaves behind a grey box with the title
'Connecting to server', it cannot be removed or moved. This happens
only in Cinnamon and not in the default Gnome desktop.

Any advice?

/Markus