I think that kicking and uppercutting powerups is a bug. My reasons will be thrown down in a number list since I'm too lazy to do otherwise.

1.) It sounds like more than one powerup is being shot when you kick or uppercut the powerup. Try putting three or more powerups on top of eachother, and than using TNT to blow them all up. Sound similar?
2.) Try kicking or uppercutting a witch. There will be a whole bunch of "splat" sounds, and than she will die.
3.) I don't think you could do this in OEM v1.00g.