Fedora 17 leave full screen mode of virtual-machine-viewer

After I've change the main OS to Fedora ( OpenSuse 12.2 with 64 bit and
btrfs always had a kernel panic and the network nearly always scrambled the GUI screen ), I still installed the latest OpenIndiana 151a7 as a KVM
guest ( the other way round didn't work for me, because my hardware is
missing EPT support, which is necessary for Illumos )

The virtual-machine-viewer allows to switch to full screen mode, but how
do I get back from full screen mode ?

I still haven't found a key-sequence, but when you release the mouse pointer
( in my case <Ctrl left> + <Alt left> ) you can go to the middle on the upper
border of the screen and a small box appears, with sending a key sequence
to the KVM guest or leave full screen mode