What's really still missing is some animations for vertical movement. That will give you proper feedback that the player is not jumping anymore and just falling down. If you take a leap from the ledge above and just let yourself fall on the mushroom, you won't get pushed upwards, either. In order to get the jumping boost of it you have to actively jump onto it.
So, it works as designed, but is lacking feedback to the player. Jump animations is already on our list (and the graphics is already prepared).