CTRL key locks in until I press it again or a shortcut is triggered

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http://askubuntu.com – When I do press my CTRL-key it seems to lock in the pressed state, even after releasing it. Symptoms of this are for example that if I press CTRL, release it and scroll in my browser window the size of the text changes. After the combination is triggered CTRL is immediatly released. It happenend to me only since Ubuntu 12.10. My Dual Boot Windows does not have this problem, so it seems to be an Ubuntu issue. How do I change this? CTRL should lose it's function instantly when I release it. (HowTos)