Staircases too. There's one of the more respected instructors up near here in northern Oregon who does civilian tactical training stuff. Which is not my cup of tea, but it is interesting listening to the guy rant. He has what appears to be a deep seated fear/loathing for staircases.
They suck all around. Going down, your legs are exposed, then your chest, then you finally have the ability to see the next floor, so your gun and your eyes don't get down fast enough to be able to process the bad guys in time before you get filled with holes.
Going up, your head is exposed, so that becomes the primary target, when people typically aim for center mass. But center mass isn't visible immediately, so head takes all of it. On top of that, the whole 360 degrees of the next floor becomes visible at once, so there's no way to take slices of the room at a time, like you would a doorway.
Staircases are very brutal. But really, room clearing as a whole is the last thing you want to be doing. You can do it completely correct, and still die. Room clearing is a matter of minimizing chances, not eliminating them.
Maybe you implied it, but adding to the 'going up' case, there is bullet ricochet -- also reffered to as skipping or bouncing bullets -- that makes it so that bullets will ricochet out at a shallow angle and ride out the wall or floor, making your head hittable without even aiming at it.
Here is a instructional FBI video talking about it.[0] And a more modern take.[1]
Imagine a handgrenade- with shotgunshells and 6 cameras glued to it. It can trigger the shotgun shells, giving it the ability to "hop" on a vector. It has a primitive friend/foe system (friends are behind the plane it was launched from) all else is foe.
You throw it at the start of the stair-case it hops up, blows the door open, enters the room, finds a target, explodes near it. All in a series of bangs.
I've heard that the stairs in castles all spiral the same direction so the disadvantage from being higher up on the steps is counterbalanced by having more space to swing your sword arm without blunting it on walls or the steps. Or at least if you're right-handed.
They taught us this in fencing as a side discussion (like during a break). Apparently it isn't true, as other commenters pointed out.
The button side of jackets thing is true though, except usually also told wrong. We're often taught in fencing that men's jackets button left over right so that a sword drawn by a right handed person doesn't fuck up your own clothing. That's also wrong, but close: men's jackets button left over right because you traditionally put your shielded side forward, your left side, and you wanted any armor pieces to overlap so that there's no holes to get caught in if you're poked from the left. Which is a stance backwards from later style one handed fencing. The not messing up clothes on the draw of a sword is just extra bonus from the original reason.
If I recall correctly, that theory is challenged by: (A) there isn't a predominant direction to such staircases and (B) if enemy soldiers are in your staircases, it's all too late anyway.
