Hey Usvatron!
Since I haven't seen your capx, I'm not sure how you create/destroy the bars. Ideally you should destroy them when the Skull is destroyed. If they're in a container this is done automatically, but, if they're not, just add a Destroy action for both bar elements together with the Destroy action for the enemy.
What is happening now is that the enemy is dead and your line 99 is setting the bar position to (Skull.X - 20, Skull.Y + 45), since both x and y are 0 (there's no skull), the bar is sent to (-20, 45). The front element is probably there too, but since its width is being set to 0, because Skull.health is also 0, you can't see it.
Hope this helps. Cheers.