Thanks, so much, Grim! Even if we don't figure it out, it beats talking to myself.

To avoid a bunch of quote tags, I've answered you in living color.
Grimwold wrote:just dropped into this thread, so I'd like to clarify a few things to try and help understand the problem.
* The problem happens only on that floor? - As far as I can tell, yes.
* does it happen if you move the floor up/down? (so the level number is different) - Nope.
* If you delete the floor, it doesn't happen on the replacement floor which would have the same number? - Nope.
* if it happens in the other room on the floor... does it happen at the exact same row? Have you tried adding rooms that are along the same row to see if it happens there? - It happens, but not in the same row or column...it's everywhere on the entire map. But see below.
* if it doesn't happen when you delete the floor, have you checked all the script entities on that floor to see if something weird got added to one of them? - Yes and, as I'm no code warrior, there's nothing funky that I can see.
* have you tried copying all the code for that level from dungeon.lua into a new dungeon? or the same dungeon on a different level? Does it still happen? - Not yet. But I'm hoping it doesn't come to that!
Here's some additional news. The mobs in that particular room are those beautiful custom slugs made by wallasaurus. If I delete the slugs, the problem goes away. HOWEVER...If I add slugs to a
different floor...no problem there, either! So what gives? There has to be a "perfect storm" of sorts happening on this floor; something else is happening in conjunction with the slugs to create this problem.
Admit it:
Now you're
really intrigued!
[EDIT @ 0906:] Correction: I tried rocks with slugs in a long corridor on a different floor and the rocks worked as intended as long as they were thrown W or S. Throw them N, and they vanish and reappear to the S of the slugs. I didn't test E. It shoudl also be noted that the problem doesn't happen as long as the slugs are not near the player (not sure of the exact proximity, but slugs halfway across the map don't affect throwing items).
I then tried replicating the problem by replacing all slugs with another custom entity: this time, Neikun's spiffy camo stoneslime01, and everything works perfectly.
My next step is to go into the files and make sure nothing I did to the slugs caused this.
[EDIT @ 0922:] I overwrote the monsters.lua with the original file, and I still have the same vanishing rock problem. I then made another room, threw a bunch of slugs, rocks and blockers in it...and that room works PERFECTLY.
At this point, I'm completely stumped. I don't even know what my next step is. I really want to keep the slugs if I can, and it's clear that the problem isn't entirely with them.