Okay, might be the top first in "Weird bugs I have in my game"
So it has come to my attention that the EAxis "Straight Molded Belt by Triumvirate Designs" and the "Straight Molded Cornice by Triumvirate Designs" is misplaced in whole lots of different ways:

• In buy mode instead of build mode
• In decorative section in deco/misc

I havent downloaded any recategorisers. This is entirely random and the only things that I've downloaded today is an ancient 2005(?) Kill Bill fighting suit for a Sim story I'm making (Which apparently is in Sims2Pack format, but it installed fine with Clean Installer) and a bunch of TheRaven's uploads. Perhaps I just noticed it today, or something made this move to deco/misc. I don't even use these things in the architecture section!
I checked in the actual architecture section in build mode but nothing weird has shown up in there. It's not a game-breaking glitch, I just need it to be in its correct place.

Both "Straight molded Belt" and "Straight molded Cornice" are listed as "Deco/misc" in SimPE. Cloning them as straight clones (just getting the resources), they're also listed as Deco/misc, and the info suggests there's no extra categorizing going on. So I'd assume that's where they are.

I've got a recategorizer by Phaenoh that puts items into proper categories, but it doesn't seem to be moving these two items, so can't say for sure.

Quickest way to check if you want to be sure is to temporarily move out all downloads (backup hoods first!) OR make a temporary test game (add a word at the back of the "The Sims 2 (UC)" folder name, run the game, a new folder will regenerate). Also check that there aren't any recategorizers hiding in the "...TSData\Res\Catalog\Bins" folder in the M&G or BG install path. Test the game, see if stuff is back to where you expect it to be. If it is, something in your Downloads folder is causing the move. If it isn't, there's either a recategorizer hiding somewhere else in the Install files, or the items are in their original place, and you're likely remembering wrong and/or had a recategorizer that's been removed.

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Sims2pack is similar to a zip file for Package files. It's possible to pack just CC in them, but most often the CC is packed with a sim or a lot.

That's the first time I noticed them being there. Why would the developers even put that thing there? It obviously belongs in Architecture. Ah well, thank you so much for enlightening me on this. :D
Edit: Yeah, it came with a Sim. With that perspective I think it's pretty common for old uploads that arent Sims, pets or lots tk be in Sims2pack format.