[1.9] Elf Patrol Train model riding a train cart is moving unnaturally fast left and right

Partner Rank: 2

Summary:
Train model riding a train-cart is moving unnaturally fast left and right.

Impact:

The model is performing unnatural fast movement and can cause the player to get confused and think the game is broken. (Game entity spazzing)

Repro Steps:

1. Download Elf Patrol from Store
2. Enable Cheats
3. Teleport to 191 104 325 (Don't move the camera)
4. Run the following command

   /setblock 165 99 325 redstone_block

1. Observe the train is wiggling 1.9.0.mp4
2. Move under the ground to see how the model is placed in the train cart 1.9.0_Traincart_System.mp4
3. Rerun the same test in 1.8.0 Client 1.8.0.mp4
4. Observe a smooth train ride

Observed Results: 

We currently we have no workaround to prevent this.

Expected Results: 
No weird movement when a model is present in a train cart

Screenshots/Videos attached: 
Yes

Regression Builds:

1346382 1.8.0.14_rc0_beta-30