Ctrl-Alt maximizing windows

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http://ubuntuforums.org – Every time I press Ctrl+Alt, it maximizes the current window. This is really annoying when I'm using keyboard shortcuts to switch between workspaces. It started happening when I used xmodmap to remap some keys (number pad, num lock), but I've undone that and I can't get it to stop. Any ideas what could be causing this? I'm using Ubuntu 13.04. Thanks (Hardware)