Comment 13 for bug 944981

This work around worked for me:

https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/858845

"Diego Cortassa (diego-cortassa) wrote on 2011-10-16: #3
It happens to me too...
It seems like unityshell plugin is rewriting the expo plugin configuration.

You can work around the bug by setting expo plugin to be loaded after unityshell:
Just edit /apps/compiz-1/general/screen0/options/active_plugins key in gconf-editor and place expo under unityshell..."