Steps to reproduce:

• invoke 'Tools' -> 'External' -> 'Configure...'
• add a new tool to the given ones and hit OK
• invoke 'Tools'-> 'External' again

Current result:

• all menu items which should have further sub items cannot be opened (if this should work, try to add the new tool to one of the given categories

Note: Restarting Creator corrects the menus and makes them usable again. This works without restarting on Linux.