Not sure if this is a bug. I haven't bought GalCiv II on Steam, but I added it there anyway as a non-Steam game. Unfortunately, when I try and zoom with my Microsoft Wireless 2000 it barely registers the input. When I launch GC2 from a desktop shortcut, this problem doesn't occur. It also didn't occur when I was doing the same thing in WinXP yesterday.
I'm thinking that Windows 7 is getting confused about which window is getting scrolled.