The Bug

The Include entities option in structure block determines whether the block will include entities inside the structure upon loading or saving the structure. Such behavior is actually controlled by the ignoreEntities NBT tag. If Include entities is set to ON, the ignoreEntities tag is expected to be 0b, as the structure block is meant to consider the entities inside the structure. However, if Include entities is ON, the tag is actually 1b, indicating that the structure will actually not consider any entities, which is a bug.

Steps to reproduce

run /setblock ~ ~-1 ~ structure_block

run /data get block ~ ~-1 ~ ignoreEntities

ignoreEntities should be 1b

check the UI of the structure block, the Include entities option is ON.