dupes jumping into solid tiles and getting stuck (8 blocks high!)

there was no ladder there to start with. they were digging a 4 high row ..

now that you mention this, this happened to me too.  I was digging a row and i think their footing got dug out from under them and they tried to jump and got stuck.  when I saw entombed it was a surprise because i could see no feet or anything sticking out, had to emergency dig to find the dupe!