The bug

The maintains_farmland tag was implemented in 23w16a, which contains blocks which should make farmland permanently remain farmland and not stop being farmland randomly if said block exists on top. Among the blocks in this tag are minecraft:pumpkin and minecraft:melon, which imply that these blocks should also cause farmland to stay farmland if these blocks exist on top. However, placing one of these on top of farmland will immediately cause it to revert to dirt.

How to reproduce

1. Verify that pumpkins and melons are members of this block tag
2. Attempt to place one of them on top of farmland

Expected results

The farmland would not be reverted to dirt by this placement.

Actual results

It is.

How to fix

Either farmland should not be reverted to dirt if a melon or pumpkin is placed on top of it, or pumpkins and melons should be removed from the maintains_farmland block tag.