Not sure if intended or exploit, I also couldn't find it using search.
Work orders seem to keep working even if you swap the building, this is my trading post after I rebuilt it from a barn.
http://a.pomf.se/veexjq.jpg
http://a.pomf.se/lfmxfc.jpg
I swapped the trading post for a barn 1 week ago, then I swapped it back today I got this.
I could see swapping every building with work orders over and over to get a ton of stuff specially since profession stuff works at level 1 skill, once you get many scavengers and geared followers garrison resources are unlimited.