You can walk on other people on z-levels below you to avoid falling. You can use this to do incredibly silly things.
To fall onto people.
Began human centipede. Became legion.
(Found using the "Show Server Revision" verb under the OOC tab.)
Server revision: release -
74da4f2e4f04a6b74d7886b6305bbb3333a36947
(Location if it's a mapping issue, screenshots, sprites, etc.)
I demand more cookies.
I'm inclined to ask how you figured this out lol

It's a videogame tradition.
Very carefully. I went ahead and ran my own instance of the server and just ass-spawned normal mobs below me and effectively made a bridge of people as well.
I _suspect_ it may be because it only performs the "do you fall" check when you _enter_ an open space tile. So when you step onto open space with a dense object (such as a person) below, you don't fall, and it doesn't re-check while you're standing still, so the person moving out from under you (or the canister being pushed from under you, or similar) doesn't cause you to drop, and when you move onto its new tile, you're moving onto a tile with something dense below so you don't fall, and so on and so forth.
Well there is also the whole thing of being able to just drive a cargo trolley in the open air. Crash through the railing and drive around in open air.
More or less.
Can confirm this issue. Had it happen a few weeks back but forgot to report it. There was a small pileup in a stairwell near medical trying to treat a crew member who couldn't make it to medbay on their own. They tried to run down the stairs and ended up running on top of people below until they ran over an open tile and smacked down on an empty roller bed with a broken leg. Rather convenient if you ask me...
Other fun stuff you can do:
Amazing. This is the future