Hi "Honest Mistake", and thanks for your tip.
The correct crashing button was "Preferences" ! It solved the problem for me too.
If anyone encounters the same issue, I recommend writing down which plugins are activated before crashing Compiz : because the crash will cause all the plugins to be disabled (even the most basic ones, such as moving windows). It took me some time to reset all properly.
Even if the solution is weird, I guess the topic is solved.
Thanks again, Honest Mistake.
Sony VAIO serie E : Intel Core I5, 8Go RAM. Linux Mint 17.2 Cinnamon 64-bit