Right clicking on same Hierarchy item duplicates the popup menu

To reproduce:
1) Run SB
2) Right click on the root object in the Hierachy view
     -> popup menu is displayed : OK
3) Move the mouse to the left a few pixels outside of the popup menu
4) Right click on the root object again
     -> a second popup menu appears : BUG (see Snapshot.png)
5) By repeating 3 and 4, you can get many instances of the popup menu

Clicking outside of the hierarchy makes all the menus disappear.
So it's a minor issue.