In 1.12, a villager will detect doors (house) up to 3 blocks above the ground level they are standing on as documented by the wiki: https://minecraft.gamepedia.com/Tutorials/Village_mechanics#Housing
This is used in many villager breeders to allow them to be turned off by moving the villager out of range of the doors. This is also used by many iron farms designs to enable the manipulation of villages and allow them to be stacked to increase the rates of these farms.
In 1.13-pre1, this detection range seems to have increase to 4 blocks. This means that many villager breeders will continue to produce villagers even though the player may assume their breeder is off which could be detrimental to their world due to the increased entities. This also breaks many iron farms that work just fine in 1.12 and will require rebuilding. This is a non-trivial task as many of these iron farms rely on precise positions of villagers at particular timings for them to work correctly. This change will mean a lot of reworking for technical players in 1.13.
I believe this changes the census area from 32x32x8 to 33x33x9.
I've attached some screenshots from 1.12 and 1.13-pre1 showing the issue as well as a world download of each. Please note that when moving the villager out of range you need to wait for a little while for the village to deregister. I don't know the exact timing of that but if you wait 5 minutes that will be plenty.
I've also made a video showing the issue here: https://youtu.be/s-VzpcRLdJc
After posting the above video I was shown bug MC-123055 which maybe related but its marked as resolved currently.
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Yes, I understand how the breeders work. The issue here is the detection range of the villager has changed which breaks existing contraptions. If we want players to upgrade their world (which I assume we do) the upgrades should limit as much as possible changes that may affect existing builds. For a simple villager breeder then it's an easy fix but for some of the non-trivial iron farms this is a big problem. I would say, unless there is a good reason for changing this mechanic then it it should be kept as it is in 1.12.
this changes makes the radius more symmetrical and benefits the creation of iron farms, more villages with a single villager
@Koala_eiO Why do you consider villager breeders to be an exploit? Those use 100% intended features and with this bug they'd only have to be rebuilt slightly, but they'd use the same mechanics regardless.
I agree with @@unknown: breeder can still be done, but this break existing contraption (and big one, that's the problem)
Personally, I hope this is "working as intended". The adjustments needed to fix existing iron farms and breeders are fairly minor, and the increased detection range makes an even larger iron farm possible since a single villager can detect and maintain 4 layers of doors instead of the previous 3. A much more serious problem for existing iron farms is MC-134166
Curious to see if this gets fixed as it breaks all currently used village mechanics. Why isn't this assigned? One of several bugs that shouldn't have even made it out of the snapshots. Breaks an Iron Golem farm I've been working on for months on my patreon server for example:
Example: https://bugs.mojang.com/browse/MC-132703?jql=project%20%3D%20MC%20AND%20resolution%20%3D%20Unresolved%20AND%20text%20~%20%22village%22%20ORDER%20BY%20updated%20DESC
coschevi
To be honest those breeders are an exploit so I doubt this change can be seen as a bug.
This is because the village checks its population in an area too small. The bulk of the villagers are in the area outside of the counting box but still inside the village sphere and that allows them to breed indefinitely while keeping the village population to 1.