Got about two rows into Tetris before it hit a bug (pieces dropping in the wrong place, and appearing as overlapping other pieces, and then a piece stopping right above a gap instead of going into it...). Did not look further.
Thanks so much for the report — You nailed it: after a line clear, the cleared rows stopped redrawing, so later pieces looked like they landed in the wrong spot or overlapped. It's a rendering glitch, now fixed in both the demo and full version. Give it another try after a refresh, and thanks again!