http://bugs.winehq.org/show_bug.cgi?id=35050
--- Comment #2 from Anastasius Focht focht@gmx.net 2013-12-04 15:58:31 CST --- FYI: I just did a Steam install with Dec. 03 client update in new 64-bit WINEPREFIX (like your system) and could successfully log in after entering the Steam Guard authentication code.
So your problem seems an isolated issue.
$ wine --version wine-1.7.7-307-g652c899
Regards