Hi Wolfgang,
Ahh, yes-- then it is not supposed to work. The -P versions of our parts do not contain HDCP keys, that is their only purpose.
For transmitters though, we don't really sell the -P anymore since you can't decode protected content with them so we don't require an HDCP license for keyed transmitters.
It's possible that because the encryption doesn't take on the transmitter then the TV decides it's fine that authentication doesn't work. I imagine each device could handle this differently and that is what you are seeing.
Dave