Logitech g29 shifter, potential knob problem

I just bought a logitech g29 shifter.

In this shifter, there are two knobs, that you spin them in order for the clamp to come up, and secure the shifter to a mount – a desk for example.

Once you are finished with turning, then you press the knob in, and it stays down.

The thing is, one of my knobs works exactly like that, but the other knob will not stay down when i press it.

Is this normal behavior? Or both of them are supposed to stay down when pressed?