I was running Tier 3 of the Ruby Phantom gate again, and on Depth 20 I decided to test the 1-way gate by trying to drop the key on it. (I was bored) The first time, it dropped right on the gate. I dropped it again closer to the wall, near the lower corner bit, and it dropped behind the wall. I already sent an F2 report, and the immediate problem (inability to finish the floor) was solved, but I figure I could put it in here as well, as there's a bit more detail in this post than in the F2 report I gave. I have also linked an imgur picture of a screenshot of the issue I discovered.
http://i.imgur.com/G06QA.jpg