I use Emacs and just switched to Cinnamon when upgrading to Trusty Tahr. It somehow stole the control-space keybinding, which I use in Emacs a lot; it is used for setting the current mark, so I can cut or delete a region of a buffer. This is also used for the autocomplete feature in Eclipse, which is one of the main reasons I use Eclipse.
Solution found: some built-in thing called IBus binds that for setting the input method. I like the input method I already have set up & I don’t need to change it, so here’s how to disable that: answer on askubuntu.com.