Joakim Andersson

I ran some tests on a mushroom buffet world without getting any results. However I also created a test world with the same seed as the survival world. I went to the island and spawned 8 villagers with 8 beds and one bell (in the same locations as in the survival world), all villagers were a part of the same village and had a claimed bed. I also made "bridges" from the 2 beds that were located in "the ocean biome spot", I firmly made sure that the bridges had a light level above 7. 

I ended up getting some what must be sieges (about 15 zombies within 4 seconds) spawning with a rate of roughly 10% each midnight tick, one siege even managed to spawn all but 3 zombies under water, the rest converted to drowns. The rest of the sieges spawned in different locations inside the mushroom fields biome (as well as on top of the village center). Sieges only occurred when I as the player stood in the ocean biome, I tested quite a lot with the player being in the mushroom fields biome, altough I got no results.

I've got the world used in the test uploaded if it is of interest

https://www.minecraftworldmap.com/worlds/_H5V5

https://www.minecraftworldmap.com/worlds/e3z0C

This one should be considerably smaller and only have the necessary regions loaded.

https://www.minecraftworldmap.com/worlds/a4NS7

I believe that this ZIP-file should be accessible as well as downloadable.