There is a bug where villagers will restock houses with resources that the house already has. It can get quite extreme as seen below.
The surplus luxuries do not contribute to luxury tax. I did the math on this and the expected income was 1653.4, actual income previous month was 1652. Given I have many houses with far over the normal luxury amount I would be over by 100s of gold if the surplus counted.
The surplus items do however count against town resource limits. Can see below, when I demolish the house the resource counts drop.
All of the extra resources past what is intended to be stocked are dropped onto the ground. Another bug here, books do not get picked up off of the ground, they stay there until they despawn. Paper has the same issue, although can be picked up by at least book binders if they need to stock their building.
7 months later everything has been picked up aside from books, which haven’t been touched. These screenshots are from an earlier save hence the different resource counts.
I can’t consistently force the restock to happen; but I have noticed a similar pattern that usually coincides with it triggering. It seems to occur sometimes after the occupants of a house change. I’ve seen it occur immediately after a house is on fire, after a relocation and after a house upgrades. All of these cause the house to be unoccupied temporarily before getting new occupants.
The biggest culprit however seems to be population reshuffles. Most of my settlement is fine and has little to no extra luxuries, even in houses that have been built for 200+ years. Yet specific areas have multiple houses all with mass restocks putting luxuries well into the double sometimes even triple digits. Almost all of these areas occur on the housing for jobs that turn on/off based on resource limits. The houses directly outside my industry zone are the biggest offenders. I assume what’s happening is when its reassigning villagers based on jobs they’re shifting to new houses often; and when they change house there’s a chance they’ll restock when they shouldn’t. The houses in specific areas shift population around so much, they just trigger this chance far more often.
This was the same year I rebuilt this house. It already had multiple restocks, the population shifted around and it’s new occupants immediately restocked it again.
House tier does not seem to matter, the same behaviour can occur on basic shelters. I haven’t tested mansions, since I don’t have any built in this settlement.
I am running two mods, but this behaviour was present in my settlement long before I started using mods. I still have pre mod saves with the mass house stocking present. I checked a few late game saves from other maps I have played, and the same behaviour is present on all of them, although to a much smaller degree. The biggest difference in this save would be making much more use of resource limits. Which is presumably what’s contributing to the population reshuffles and triggering the bug so regularly on this save.