If rdesktop looses the connection it won't release the keyboard and thus no other X application will be able to receive key events. Sometimes rdesktop will also grab the mouse.
See:
https://bugs.launchpad.net/debian/+source/rdesktop/+bug/81854
https://bugs.launchpad.net/ubuntu/+source/rdesktop/+bug/217868
http://bugs.debian.org/317068
etc.
Any news about this bug?
It also happens to me, Fedora 17 (x86_64), rdesktop-1.7.0-2.fc17.x86_64