Steps to reproduce:
1. Open new unity project
2. Open asset store, deatach window and maximize it
3. Download "Shadowgun: Deadzone GM's Kit" asset package from the store
4. When prompted to import it (after downloading, second import screen), do so, and try to move and close the asset store window
5. Observe that the Unity has crashed

Note: Does not seem to crash with other parts of the editor (maximized, docked and undocked). Or with asset store docked.

Also crashes with "Angry Bots" asset package, possibly with other big packages.