Please see attached snapshots and test program. The program set font size of the Menu to a non-default value. When the menu is near the edge of the screen, the sub menu doesn't adjoin its parent menu.

This is found with 8u40 and reproducible with 8u20. But 8u11 works fine. So it could be a regression.
It only happens when the menu is close to the edge of the screen, then the sub menu wraps. When font size is smaller than default, the sub menu keeps away from the parent menu, but when font size is larger, the sub menu overlaps the parent menu.