Grimrock

In the skyway room, I remove the items from the pressure plates so that the door opens and I can go up the ladder to look down on that same room. I drop a rock and a sparkle floor tile appears in front of me. As soon as I move forward I fall through the tile and back to the room below. Is this a bug? Or am I doing something idiotic?

Yes, it's a bug. It will be fixed in the upcoming patch. Meanwhile, use something else than throwing weapons.

Removing any rocks from all character hands might do it too.
(never had an issue here with rocks)

Turtle steaks and bread loaves did the trick. Thanks!