Cannot edit menu item

It isn't possible to edit the menu item for "Your Referrals" in /admin/build/menu.

The attached screenshot shows what happens when you try to (click edit). I have seen something similar to this before but not in 5.0, it was in 4.7.x somewhere and it's bugging the hell out of me because I cannot remember where or when!

The "restrict access permissions" in the bottom half of the screen is the menu per role module. Turning this module off does not solve the problem.

Any help in solving / patching this would be greatly appreciated as always.

Regards

Patrick