It's a issue of bad memory management with .ESPs. If it was an issue with the game itself, then why does it never happen with vanilla interior/exterior cells? Even if it IS an issue with the game itself, it still heavily affects user-made mods, and therefore deserves a place on the list.
So why have I never seen it with any mod that contains interior cells? What version of the game are people using? Does it do any good at all to post a bug when we don't know what CK version OR game version someone is using? Why report issues with CK 1.5.24, for example, when that's not the one that's currently available for download? Why report bugs in game version 1.5.26 when that's not the one that's currently available for download?
Yeah, I know, I'm probably being really super pedantic about all this, but taking reports from anyone who is refusing to update is just plain silly. There's no chance in hell Bethesda would ever take a report against an old version of the program seriously, so I don't see why we should either.
So I'd suggest that any report made where the version of the CK *AND* game is not specified should be ignored and left off the list until that information is supplied. I think that alone will cut down on the number of issues being reported. There's too many people right now continuing to report things that later versions of the game and CK are known to have fixed.
The CK clearly doesn't have a problem with you generating a dungeon with however many pieces it takes to trigger this. Only the game has issues with it. So there would be nothing for Bethesda to reproduce on the CK side of things. This isn't like the Navmesh bug which was a hybrid issue when it was first posted to this list. Technically it should have come off at CK 1.5.24 when it became clear the remainder was a game-side issue.