OHHHkay! I see what you mean, so releasing the jump button shouldn't immediately send her down, but more stop her ascent for a brief second before descending! Alrighty! I'll see what I can do about that!
I don't think even equipping the Power Ring should have any effect with the damage calculations when killing enemies and bosses, but this still does concern me, so I'll definitely look into that.
Oh, and that mine cart falling into a pit thing, do you mean when you touch the rails you still fell through? Or do you mean when you fall into the pit you hear the landing sound and still die?