[bryondowd]

Haven't seen that bug happen so far. Wonder if it's just a case where someone had already mined out one of the tiles that should have been an up/down, so all the game could do is put a down stair. That said, I only really use stairs for exploration or project tunnels, and it's all ramps in my fortress proper.

I did notice that it seems like dwarves won't/can't dig straight up with stairs, they need another path up. Not sure if that's new or pre-existing limitation, as I haven't played classic in over a decade.