It's not a major bug, but I do know it can be done in all three versions of Mario 3. But it's easiest to see in the NES version. In level 1-5, the first underground level of the game, with fire power, go to the last part of the cave, where you see the Venus Fire Trap and an upside down plant. Go to the slop, stopping about half way up, turn and look back towards the left. Jump and shoot your fire balls, you should see them go up through the ground heading for the pipe. I first found this a LONG time ago, and have tried it in every version(SMB3, SMAS and SMA4) and it does work.