Hmm, were you playing the game fullscreened? If not, the up/down arrow keys will ALSO scroll you up and down on the webpage, which is unplayable. But fullscreen fixes that.
The phasing issue you described is a bit concerning, too. The blocks are supposed to disappear only once they're about an inch "below" the bottom of the screen. I wonder if it's a resolution issue, and you're seeing further down than intended. Not sure.
Well, thank you so much for your feedback, and thanks for playing!!