The player is basically falling through the floor while landing after a jump.
It happens in the browser on the phone aswell as in a packed apk from phonegap.
I did NOT had this bug while testing the game on my PC.
Here is a link to a page which contains both (apk and/or browser version):
Is this a bug, could this be due to some 'framedrops' on the phone or is this badly evented?