At Christmas I booked a GVA-ZRH-TXL and return on all LX metal and was surprised to see an Amadeus PNR visible in LH and M&M. Ah, I thought, finally LX has integrated its EDS with that of its parent company.
Wrong, my latest booking, a GVA-LHR, doesn't exist outside LX.
I suspect that as the TXL flights are code-shared with LH, there has to be someway for LH and LX to share reservations, which is why the reservations get allocated an Amadeus PNR.