If one sets a sprite to "auto mirror" and then rotates it to 180 digrees to create the left facing sprite and plays an animation other that the first animation, overlapping detection is clearly detecting overlaps based on an incorrect collision mask (perhaps the colision makst of the first animation)
open the CAP I've attached, run in and use the arrow keys to get behind the enemy, then face it and press the "Z" key to attack it. You will see that the overlap detection is so off that one needs to practically stand perectly inside the enemy for the enemy to react from the attack, yet the attack always works perfectly from the left side of the screen. (because the sprite is not rotated(mirrored)
example of the bug