Can't use single click in inventory

Put the summary of the bug you're having here

What I expected to happen was...:
I went to shift-click to apply armor...

What actually happened was...:
Nothing happened, so I tried to single click and move the mouse to the slot. Nothing happened. I have to use click and drag to interact with any UI.

Steps to Reproduce:
1. go to any 1.8.1 prerelease and try to interact with any inventory-related objects.
2. Shift-click won't work
3. ...