I got the glitch again, and I can describe it with more detail:
When I got the second +8% health powerup/item, my health started to go down by itself until only a few pixels of red could be seen on the health UI. After this, enemies couldn't kill me, no matter how many times i hit them.
Also you can't pick up the gold mineral of level 2 after mining it. It follows you, but you don't pick it up.