I've noticed that some items that I've pickpocketed are not marked as stolen and I can freely sell them to any merchant that buys that item type.
It's not all items of a specific type. For example, some stolen necklaces are not marked as stolen and some are.
Some examples are Calcemo's Ring, shields, imperial bows, and lots of random jewelry. Basically, anyone unfortunate enough to walk past me gets their pocket picked.
Is this a bug? Could it be a side effect of a mod? Or is it some game mechanic that I don't quite understand yet?
I play on PC with Hearthfire and Dragonborn DLCs.
Note that I've never given any of these items to a follower or put them in a container of any kind. I've also never used the fence items option of the Amazing Follower Tweaks mod.
I've tried starting a fresh game with no mods installed and it still happens. So, it doesn't look like this is caused by a mod. I guess it'll just be a mystery. It's a beneficial effect, anyway.