I've also encountered the glitch
I have the same problem as vilexis.
As soon as I get the slingshot Gretel becomes impossible to control. She continues to run either left or right [mainly right] and at times only the left and right arrow keys [a and d keys] will work, but as soon as you let go of one she will run what ever way she is determined to run to.
I love the art and style, but I agree with vilexis, it's hard to enjoy it when I can hardly play it.