Taggerung

Zombie pigmen share the same spawns_on_block_prevented_filter and also will spawn on the nether wart blocks within the fortress.

This bug did not negatively impact my gameplay but I did experience it yesterday. 

Long before I had stashed some cured villagers (originally spawned as zombie villagers at night) in an open but protected area with access to beds and workstations. The only accessible workstations were brewing stands and cauldrons. A named villager, Bill for reference, chose a cauldron for a workstation and I elected not to trade with him for the time.

Some day cycles later, during a night upon luring another 4 zombie villagers into the area (lucky herd spawn) they proceeded to re-zombify the inhabitants including Bill. I captured all in boats and began curing each of them again. The primary occupation I intended to get use of was cleric as I wished to trade my rotten flesh surplus. I noticed Bill (not having locked in trades as a leather worker) elected for a new occupation as a cleric. However when I went to trade with them their trades were still that of a leather worker. I attempted to break the workstations and replace them but the same results occurred.

Amused on what was happening I decided to keep things as they were and traded with Bill to get them to master level. Here as you can see in the trade menu Bill is a max level cleric with the leather worker trades still.

v1.16.221 Windows 10

I've ran into this twice now and only going to the Nether out of MANY trips - I was able to Elytra+Rockets back to the expected Nether location but was very weird and I initially thought I did something wrong.

I've encountered this same issue on 1.16.100 WIN10 edition. To fix I've used a bucket of water to gently nudge the bee off the space it is stuck above.