The new /ride command which was added in the latest snapshot breaks if used in a repeating command block, causing what I think is a server desync. The player is unable to interact with blocks or entities, and other players will see them still riding the target.

What Should Happen:

The player should be permanently riding the target entity while the command block is active.

What Happens:

The player is never mounted on the entity, instead just teleported to its location. The player can even move away from the entity, but gets teleported back when the shift key is pressed (like a controlled lagback). This process will repeat indefinitely until the command block is disabled.