mono/MonoGame — pull request #1710 by tomspilman (2013-05-03 22:49:25+00:00)
Title: WinDX Support For Left/Right Control, Shift, and Alt Keys

We had to switch over to using WK_KEYUP/DOWN events to properly capture the control, shift, and alt keys.

I'm unsure about suppressing the system menu here, but it does allow the alt key to be captured.