I I flew on Germanwings from LHR to TXL last month. I connected through LHR instead of MUC/FRA due to price. The ticket was United issued (016).

The Germanwings segment did not automatically post so I wrote in for missing milage credit (RDM/PWM/PQD) and provided copies of my boarding passes and the receipt from the UA site. I received the RDM (590 - no bonus), PQM (590) and PQD for that segment within 2 days.

Also, I was able to use the *A lounge at LHR to shower and eat breakfast so I didn't experience an issue with lounge access.