Entities resting on a happy ghast fall through when a player is not standing/hovering above it

When entities are resting on a happy ghast and a player who is standing/hovering above it moves away a sufficient distance, all entities resting on the happy ghast fall through.

To reproduce:

1. Summon a happy ghast (NoAI optional for easy testing)

   /summon happy_ghast ~ ~ ~ {NoAI:1b}

2. Stand on the happy ghast or fly and hover very closely and directly above

3. Drop items and/or summon entities

   /summon pig ~ ~ ~

4. Fly/move away upwards or to the side

   1. Expected behavior: All entities currently resting on the happy ghast stay in position

   2. Actual behavior: All entities resting on the happy ghast start falling and may intersect the happy ghast collision and get launched at different angles.