I searched the forum and couldn't find any mention to changes to this area, but some of the best pieces seem to be insta-crumbling. Is this a code change, or something I'm missing in what I'm doing?

Assuming its the items I think you are talking about, there was a bug with them that prevented them from maintaining their rot_death status as they were supposed to when they were assigned to an owner.

At some point within the last few years, that bug was fixed (perhaps incorrectly) so that the items should now crumble when you (their owner) not the mob that had them dies.

Either way, if you haven't put it on the bug board yet, please do.

Cause they definitely rot basically immediately (so rot_death on mob that holds them).

That was seriously one of my favorite items in the game, and after the change, I just assumed along with everyone else that the change was an intentional nerfing of the item. But the speed at which the thing crumbles left me wondering what the hell was the point of even having the item in the game anymore. I should have known it was a bug. Wish I had posted it myself like, a year ago.