Neat game. One thing you need to add is keyboard controls too if you plan on ever putting it on a web browser or Construct2 arcade. Just add keyboard object, right click your touch conditions and add the appropriate arrow key then right click the tiny space to the left of one of the conditions and choose "make -OR- block"
I finally got it to do what your were referring to, it doesn't do it all the time.
Most likely this is being caused by one of the animation frames not having a collison bound setup.
My recommendation is to make a player control sprite that is set to invisible, all your movement options, collisons, and damage options etc should use this invisible sprite. Then pin your actual player graphic sprite that has animations to this invisible sprite. Now you don't have to worry about animation frame collisions since all this is being handled behind the "graphics". It also makes tweaking collision bounds soo much easier since you only have to do it once!