Hitboxes of riders don't move with their rider when the mount rotates.

Partner Rank: 2

Partner Team Reporting: Noxcrew

Verification builds: 1.9.15- 1658980

Summary:

For a boss fight in our next map in production, we wanted the boss to have three warts that have to be shot off by the player to progress. We did this by mounting three entities to the main boss mob, and will be offsetting them to put them in their proper place. In our tests, I noticed the riding mobs seemed hard to shoot. "/bounds" diagnosed the problem. As the boss, which cannot move, turns to look at the player, these riding warts will visually move as they should, but their hitboxes do not move. If you teleport the boss to face a new location, the hitboxes seem to properly relocate. If the mob is actually walking and moving, the issue seems to correct itself sometimes.

Impact:

On our current project, we're needing to restrict the way we're using this mechanic, and it's causing us to have to dumb down the fight. Even in this reduced state, it's pretty likely players will run into an issue where they are shooting at these warts but not hitting them. Please see the video for the extreme example of this.

Repro Steps:

1. Ask for the hitboxbug.mcworld from @greggo on slack
2. Load the world, /summon horse
3. /bounds
4. Look at where the hitboxes are, then move around the horse in a circle. Notice the boxes do not move. [NOTE: Sometimes, infrequently, they will appear to move. Attempt to shoot at a hitbox if this happens, I found that it's always a visual error if they do move]

Observed Results:

The hitboxes do not move as they should relative to the position of their entity, and as a result, shooting said entity with a bow and arrow does not result in hitting said entity.

Expected Results:

Hitboxes should properly follow the visual location of the entity continuously and consistently.

Screenshots/Videos attached: 

https://drive.google.com/file/d/1b0GzOrIFLjiQx7E8Y1FPi-6u42kJB0Hb/view

 

Regression Builds:

I have no reason to believe this has ever not worked this way.