It seems that the problem is in the rotation at 4s. The pivot point is taken about the rail component, not about the model. This somehow links the small component to the big one further on.
Currently, it is a little bit cumbersome to specify the basis for the rotation pivot. You have to right-click and choose to which object (or model) it belongs.
In the attached modified model, I modified the rotation.
DotSketch - Test - modified.skp
Fredo