Phantoms despawning in day with PersistenceRequired

I have a need for phantoms that do not despawn during the day. I just tried spawning one with:

summon phantom ~ ~10 ~ {PersistenceRequired:1}

It appears to have still despawned.

I would think phantoms would have the PersistenceRequired tag, or should have it if it don't, just as every other mob does.

This causes name tags to be ineffectual.