Note: I have applied the patch from pull request #2 .
I observed that when a piece rotates, it may end up overlapping with other blocks. I am not exactly sure of the exact conditions of this happening, but the instance I saw happened when the piece tries to rotate on or near the exact moment the piece locks into place.
I might or might not look into this further; if I do I'll post my findings below. (also can I configure the game so that I can manually control it?)