I have some cotton fiber cloth bags, which I made in the Clothier's shop using standard vanilla a w b. My Succubi refuse to move them to a Furniture stockpile set to accept "boxes and bags" of types plant cloth, leather, silk, yarn. Confused, I made a whole new Furniture stockpile, blocked all types except "boxes and bags", left all materials open -- still nothing. The bags just sit in the Clothier's shop, never having been moved since they were made.
I even made a whole new bag. A (cotton fiber cloth) was used (from some caravan), and a -cotton fiber bag- was produced. It, too, sits in the workshop. I made a second bag, and they chose a (cotton fiber cloth) which happens to be dyed red (with carmine dye). This one made a no-quality cotton fiber bag. It also sits untouched in the Clothier's shop.
Finally I tried making a silk bag. A (silk cloth) (red with carmine dye) was taken, producing a -silk bag-. It sits there untouched.
I made some lavish meals, which freed up some bags that were in use to hold quarry bush leaves. These bags got stockpiled.
What's the difference between the bags that are being stockpiled, and the ones that aren't? No burrows have been created at all yet. None of the bags are forbidden. There are no pathing issues, since the Succubi can get to the Clothier's shop to make new bags.
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Well, damn. That's embarrassing. The difference is there is another stockpile somewhere out there taking from the Clothier's shop. It's not even a Furniture stockpile. It's a finished goods stockpile, taking clothes.
I added a "take from workshop" link to the Furniture stockpile, and now it's working.