Unexpected physics behavior: Model moves together with another despite collision groups being disabled

Hi everyone,

I’ve attached the file bug.rbxl. It contains two models: “Car” and “CarWithVelocity.”
They are completely identical, except that CarWithVelocity has a Velocity set on its DriveSeat that pushes it forward.

Both models are placed in the exact same position.
The problem is that when CarWithVelocity starts moving, the Car model also moves along with it — even though collisions are supposedly disabled.

I have a CollisionGroup called “Car”, and it’s configured so that “Car” has no collisions with other “Car” objects.
I’ve double-checked — every part in both models is assigned to the “Car” CollisionGroup, and the setup looks correct.

Yet, CarWithVelocity still seems to push or pull Car somehow.

Does anyone know why this happens, and how I can prevent Car from moving along with CarWithVelocity?

Thanks in advance!
bug.rbxl (125.7 KB)