I'm playing with the Steam version of W2EE on Windows 7 x64, I5 3570k, Z77a chipset, 16GB RAM, Logitech G510 Keyboard, Raza Naga mouse. I have all of the latest drivers.

When I select an item in inventory using either the space bar or clicking the selection acts like a double click. Sometimes more than one item is moved to inventory or sold. In dialogs and menu selections it acts like a rapid click through.

Does anyone know of a User.ini setting to fix this?

I don't have this problem in Windows or other games like Grim Dawn, Diablo 3, Everquest Landmark and Civilization 5.

I want to keep using the Steam version so that I can unlock the various achievements.

I am having this exact same problem, however I am using the GOG.com version. It doesn't happen all the time, but it does happen a lot. It's exactly like you said - Sometimes more than one item is sold, or dialogue gets skipped. Doesn't happen in any other game.

Anybody have some advice for us?

Someone on the Steam forum told me that it was related to AMD's Raptr software. I haven't tried to disable it yet as I've been playing and doing other things with my spare time. If you are using NVidia's version try disabling/exiting it while playing.