Did not find a thread for Dota 2 Store (not in-game store) so posting new one. Happened on 16/08/2013 around 10 a.m.
I purchased keys to unlock some chests and after unlocking the chests when I double-click on the purchased item it followsd my mouse cursor. Afterwards if I double click any other item and it stays on screen where the item was originally located. Restarting Dota 2 fixed the issue but I purchased a key just to see if its a reocurring bug and sure enough it happened again.

My video settings and system specs when the bug happened:
in-game 4:3 a.r. 1024x768 res. Windowed mode. V-sync on.
desktop 16:10 a.r. 1680x1050 res.
AMD Phenom II X4 965 BE 3.4GHz @ stock speeds.
XFX ATI Radeon 5870 1GB @ stock speeds.

To reproduce the bug:
1. Purchase key from Dota 2 Store.
2. Unlock matching chest.
3. Double click the item that dropped from the chest.
4. Double click any other item in the store.

Here is the image of the bug:

Hope this helps