That would explain some problems I have with the tuner reception quality (I have a BMW with build-in diversity antenna which used to very good with my old head unit).
Sometimes when switching on in tuner mode or when changing to tuner mode, the reception quality is quite low.
I then change to AM and back to FM which improves quality significantly (audible and visible on the display).
Maybe I should mention that I have hooked up an additional TMC-Receiver to the antenna. I'm not sure wether this could influence the antennas operation, therefore I never reported this behaviour. After the "little push" the reception quality is always very good, so I don't bother too much.
Now that I think about it. When first installing the tuner module, I forgot to connect the antenna amplifier. That got me a low reception quality quite comparable to the one described above. So it could very well be that the antenna amplifier just isn't powered sometimes. I'll try to pay more attention to the circumstances in which this happens.

Wolfram