Super Munchkin Theft Ability

[Captain Pandaman]

I had a small disagreement with a friend over the rules for the Theft ability granted in Super Munchkin.
Does that version act exactly like the Thief class ability and can't be used on somebody during their combat or yours?
My friend is firmly convinced that he can and is the owner of the Super game we play so I let it go, but considering he has won 3 games from using it to steal during his or his victim's combat I would like to know the official ruling.

Thank you in advance for any answers.