On Sunday, June 16, 2019 at 7:31:29 PM UTC-7, wrote:
When we met up north of Leyba on today's flight, I was getting a dual return from your ship. Apparently, one was Flarm and the other was ADS-B. No problem, though. It was just a bit unusual.

The suspicion then is the PowerFLARM does not have the correct ICAO address of the glider in its configuration file, we know the ADS-B is correct, because it's a certified install that had a performance report pulled.