There is a stray black box on the "Edit DMap" window.
Steps to recreate:
- Quest->DMaps
- Click 'Edit' in the "Select DMap" window
- Make sure "Type:" is set to "Overworld"
- Observe black box immediately above the "Continue here" checkbox label
Upon closer inspection, it appears to be the horizontal scrollbar which is only scrollable when "Type:" is set to:
- NES Dungeon
- Interior
- BS Overworld