I've replayed the Bird fight like 10 times because of this but I found a solution.
After you defeat the Bird happens next:
- player is frozen and can't be controlled
- a leaf spawns right above the player
And now the game waits for the leaf to fall on you. After this you obtain the new ability and controls unfroze.
BUT. Those platforms are still up and if you're standing under one them guess what. Yeah, the leaf falls on a dang platform soft-locking the game forever.
THE SOLUTION TO THE BIRD BUG: just make sure that after the last hit there is no a platform above you