If you've updated to a GNOME 3-using system, you'll see endless "tiling" of the Steam login window, primary window, and installation windows.
This can currently be alleviated by switching the bottle type to "windows 7" in wine configuration (inside Manage Bottles>Control Panel).
If you've upgraded to GNOME 3 and don't see this issue, please file a ticket!
http://www.codeweavers.com/support/tickets/enter/
or send an email to info@codeweavers.com referencing bug 8513
Thanks!