Bullets Disappear While on the Elevator
If you're standing on the elevator that drops you off on a new floor it seems the bullets get blocked by invisible walls. As soon as you step off the elevator tile, you can shoot through it just fine. As soon as you step back on the tile, however, my bullets disappear and don't hit enemies. I'm using the Cryotech Alchemer MK II, and the bouncing shard that breaks off functions normally, but the primary bullet doesn't seem to even exist.
I don't know if this bug is related to the gun because the bouncing projectiles have some odd effect, or if it happens to all guns.

This does seem like an old left over from earlier times. I'll bring this up. Thanks!

Isn't the elevator a safe spot?
Letting people shoot out of it seems like a bad idea if monsters can't get in and eat your brains.
As I recall, the slimes were all over the elevator trying to eat me. I'll test it out as soon as a new dungeon is released.
So monsters can go onto the elevator.
http://wiki.spiralknights.com/File:ElevatorNonsafety.png
Also, you CAN shoot another enemy who is on the elevator while you are. The bullets don't appear, but you do hit them. You simply cannot shoot enemies outside of the elevator spot while you are on it.
It's reasonably safe to assume all guns. I've had the same issue with my Protogun, Autogun, and Blaster in the past.