Can't set mark

Hi,

very strange effect with Ubuntu 14.04:

Usually I can set a mark (to mark a region) with Ctrl-Space under Emacs.

It does not work to set a mark under 14.04. Now the very strange part of the problem:

I have two desktop computers, one still with 13.10, the other with freshly installed 14.04. And I have a server still running 12.04.

When I login to the server from the 13.10 machine with ssh -X to the server and start emacs on the 12.04 server, I can use ctrl-space to set a mark.

But when I login to the same server from the 14.04 machine with ssh -X, starting the same emacs on the same 12.04 machine, I cannot set a mark with Ctrl-Space. So maybe it's not a problem of emacs itself, but something with the X and Keyboard environment.

To simple check this: Just start an emacs under Xubuntu 14.04, enter some text, and try to mark a region by marking with Ctrl-Space.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: emacs24 24.3+1-1ubuntu3
ProcVersionSignature: Ubuntu 3.13.0-16.36-generic 3.13.5
Uname: Linux 3.13.0-16-generic x86_64
ApportVersion: 2.13.2-0ubuntu5
Architecture: amd64
CurrentDesktop: XFCE
Date: Fri Mar 7 21:18:44 2014
SourcePackage: emacs24
UpgradeStatus: No upgrade log present (probably fresh install)