Tap your screen with a hammer, then wrap everything in duct tape.
...I got nothin'. It's a pretty interesting problem. I'll see if I can come up with something while I wait for some updates to finish loading for revit.
Alright, after a quick search...
is it possible that someone else has been using your machine. From what I can tell, it's possible to edit your double-click action in your CUI settings. If DBLCLK and PICKFIRST are correct, then....maybe someone loaded their CUI or profile and didn't change it back. It's happened to me that someone's done that, except instead of the double-click-editing, it popped up a shortcut menu everytime I clicked the mouse. Drove me nutso.
The CUI might be worth checking out.