I've read some people have been having trouble with switching between languages and I'm also experience something similar. In my case I can successfully change the key combination to switch languages and it works at first, however, after some time it no longer works. Going to "text entry settings" there seems nothing wrong. I can fix it by re entering the desired key combination but again after some time it "forgets it" and no longer works.
This is a fresh install of ubuntu 13.10.
Any help appreciated. thanks