Here are a few bugs I noticed:
*-When you restart, the underground music doesn't stop playing.
*-Inside the pipe room, you can exit through the wall instead of through the exit pipe... placing you before the pipe entrance, allowing you to collect all the coins again, and in effect making an infinite amount of points possible.
*-Not a bug, but I'd like the gameplay to be faster. It moves too slow. It'd be cool if you could add some enemys besides the plants and put in a time limit in later versions of the game.