Related and was discovered on BE testing with MC-259223.

You can use the /ride command while in spectator mode. You can do things like ride and move horses, minecarts, and boats, which is not intended, as a player in spectator mode isn't supposed to be able to interact with the world.

Also, as a result of the command, you're unable to dismount yourself from the horse unless you run the command to dismount yourself.

Step to Reproduce
1. Spawn a horse and tame them.
2. Go to spectator mode.
3. Use the /ride @s start_riding @e[type=horse] (make sure no other mobs are spawning and are cleared)

Observed Result
You can ride and control the horse.

Expected Result
You shouldn't be able to control and ride any entity.