Why this happens?
1. If you have lootomatic enabled (and you have to - or some other addon doing same stuff) AND have the loot filter enabled.
How: For. ex. Last MOB you fight before going to NPC drops two stuff: small potion + chain mail of heavens.
You drop small potion (because of loot filter) but chainmail is taken before the potion is dropped.
Then an empty space is left before chainmail.
When you start autoselling, it comes to the empty space and apparently stops (closes seller window) but due to lag or bad loop (goes 1 more time after empty slot) it tries to sell that chainmail but in this time it sends it to be EQUIPPED. Then our expensive equipment is in our backpack waiting for next time to be sold (never - NEVER put that PURPLE option to sell items to NPC xD).
If you are smart and don't put PURPLE in autosel options, you are having another problem!
Unequipping item like happening to me (2 of them) Legguards and Main weapon 4100matk with some very very 200 times wors equipment
2. If you use up all the potions that are in place after the autoloot_from. You can get the same situation as above. Unequipping items, and maybe even selling them to NPC if they are in rules set up for autosell. This should happen rarely but still can happen with significant % of possibility (being less than 1%, but still is worthwhile fixing).
-I can't say with certainty why this happens, didn't take a closer look at functions (or it has to do with updating item table - maybe should be forced before NPC?) or maybe some other thing is causing it. But it's a nasty little trip.
-Deleting all rules from loot filter should solve the first problem, but again we have the issue of used up potions after the autosell_from slot number.