Project to demonstrate overlap issue.
The larger, gray boxes are test objects to overlap the smaller square with. The white lines are drawn where the 4 quadrant borders are. Move the small square with the arrow keys to overlap a test object. While overlapping, press ENTER to print "justPressed" with trace(). If the squares overlap on a quadrant border, the keys justPressed happens multiple times. If the small square overlaps a white line it gets justPressed twice. If the small square overlaps 2 white lines (center square), it gets justPressed 4 times. This is with FlxG.worldDivisions = 1. If worldDivisions = 6, it happens in other areas too, since there are more divisions. It happens with justReleased, too.