Bug Enters 2 Letters for 1 Key-Press

My friend bought him and I both a copy of Magicka 2 so we could play together. When he tried to log into his paradox account, he couldn't enter his email or password, because whenever he pressed a key, it entered it twice. (abc --> aabbcc). This renders the online un-playable to my knowledge. He has tried copy/pasting and it didn't work.

Super Ninja Edit: He is on a Mac.