Steps to repeat:
Launch C::B (13.12)
Create new wxWidgets project
Using wxWidgets 3.0.0
Using wxSmith, Frame Based
When project opens, double click on MenuBar editor
Select the 'About' child menu item
Click on the ^ button to move it up - C::B crashes
I realize in reality one can not move a child menu item that's already at the top past its parent, however that's no reason for C::B to crash. Either a) inform the user that moving the child past its parent is dumb, or b) actually move the child item to the previous parent menu item.
In my case, I was trying to do the latter. I created a menu item which showed up as a child under the wrong parent and in an attempt to move it up to the previous parent item, C::B instead said 'No dice, I shall crash instead.' The work arounds are to either a) delete the item, select the correct parent, then create it again, or b) move the item to the left (so it becomes a parent), move it up under the parent it's supposed to be under, then move it back to the right so it once again becomes a child.
What's odd is that if you select the 'Quit' item and click the down button, it WILL successfully convert itself to a parent first and a subsequent down click will move it down and you would have to click right again to make it a child. It's the moving UP that's crashing C::B.