Yeah I know it is experimental, but I guess you guys still want input on it, right? Sometimes when alt-tabbing out of the game, the belt bar becomes click-through such that you cannot pick up / activate items on it. Instead it registers as a movement command to the position under the bar. This persist consistently until you alt-tab out and in again, where it *might* fix itself (it usually does). Keep up the awesome work!
I recommend using a program called "ShiftWindow" that allows you to run windowed games in a 'fullscreen' view. Unless you're really keen on having the Steam Overlay, this program works wonders for alt-tabing.