3D Models follow terraforming even with Snap To Ground disabled

Hello

I brought a 3D model to my scenery and disabled the snap to ground option.

Then I created a terraforming polygon to tune the elevation underneath.

However, despite having the snap to ground disabled for the 3D model, if I move the terraforming poly up or down to raise or lower the terrain, the 3D model follows.

Is it like this by design or a glitch?

Any way to keep the model as I placed it?

Thanks