Only pirated versions of the game released by a certain Razor group has this problem with the mouse where you can't click certain items in the interface. The legit version does not seem to suffer from this problem.
....So yeah. Zing.
Wow, I guess they've been distributing their cracked version over Steam then. Oh wait...
The interface works with the mouse *most* of the time. There are random moments where it will not respond to the mouse at all. Closing out the menu and reopening it fixes that issue.