Level 64 cannot be solved anymore. v0.0.5 doesn't accept a stone leaning on a stair as "lying down". The unneeded ladder you removed was placed there to make it harder to find the solution. It also lets people keep playing after accidentally falling to the lowest ledge. So it surves two purposes.
Well okay, I've now seen the comments in the older ticket that caused this behaviour change, and after seeing the tumbler grab trick in the solution of level 091 SNES, was able to solve the level.The Amiga version is completely solvable without the tumbler grab trick. Would make sense to add a second level 64 where the stairs are moved one step left so it is solvable without the tumbler grab trick, or to change the game logic back. It is strange that you didn't change the rule for stopper stones, where stones leaning against them still count as lying down.