Sometimes you have to use the up key to go down ladders and visa-versa. Very hard when you go up a ladder in a mine with the down key, only to reach the top of the ladder and then instantly jump off the ladder and fall to your doom.
If you manually place stairs (using the default sized stair block), I guess they must be off by a fraction of a millimetre. You have to use the space (jump) to walk up the stairscase. Otherwise you get stuck.
Overall, though loving it