On one system I have running Linux Mint 17.1, if all things are minimized, I can't maximize anything. I click on the task bar and nothing happens. I have to right click and go restore. Oddly, I get an option for "unmaximize" even though it's minimized. If one is already open, then I can maximize the others. Does this with any program. Occasionally it actually does work, it seems to work only once per program. Tried rebooting , updating etc. no go. I think it's Mate, but I'm not too sure, installed it a while back.