I have had this happen every time I buy something from the Flea Market or in general any purchase from a community lot, such as a painting from an easel or collectibles from a sale table.
The items appear in the personal inventory of the sim who bought them and can be placed on the lot.
A duplicate appears in the household inventory also, but it still seems to be tied to the original object, as selling it from there also removes the original. Trying to place the duplicate results in a script call error popup.
Placing the original into the household inventory shows two of the same object now in a stack. You can sell the stack for double the price of the object and make a profit that way.
In some cases, I have been able to stack them in the household inventory, sell the items and the undo to retrieve one of them and make it functional again and placeable on the lot as intended with only one copy. I've really had to fiddle with it though for items I want to really keep like awesome paintings I bought from the Flea Market and don't want to lose.
No CC or mods.
This has been happening to me for as long as I recall and I've only had City Life since March 2017, so it's either been in since the 23 March patch or earlier and I only recently noticed.
Maybe related to the other bug where an item you purchase like paintings turn into ashes and you can clean them up and a duplicate may or may not still exist in the household inventory.
