如果开启选项“synch_nether_chunk_spawn”，且两个不同的主世界区块对应同一个下界区块，会导致该下界区块被覆盖生成。（区块同步部分没做生成判定？）、
另外一个问题是，选项“block_placement_allowed_outside_spawned_chunks”对下界不起作用，不清楚是否故意为之，希望添加一个开关，谢谢

是的，关于第二个问题，这个选项的确在下界不适用，就好像没有被开启一样

This is not intended, good pick up. Looks like I missed the check for spawned chunks from this situation.

I'm not sure if my understanding is correct regarding the second issue - is it that the option doesn't apply in the nether? I'll raise a second issue for that.