Wow. That is absolutely awful. I just played a few rounds and every single death was from losing my timing after a transformation stop in the middle of a jump or something. Such a bad gimmick. Makes the game unplayable.
Can't say that's ever happeend to me (in 30 minutes I just spent playing the game). I find it more annoying when a double jump that seems legit at the time ends up sealing your fate.
It has happened to me numerous times. When you transform you lose all momentum and start from almost no speed. Being that the stars are many times right at the edge of a jump, if you dash to break the star, and jump, you transform mid air. After the transformation you are left moving very slowly and falling through the air, this makes recovery difficult, and disrupts the normal flow of a dash, jump, or double jump. You can count and avoid an edge star that would transform you, but many times they are in tunnels that you cannot jump over.
Can't sleep, clown will eat me.