Is it common practice for a NMEA0183 device to forward input sentences to its output wires?
My ICOM M604A VHF radio does this. It gets GPS position info from my NMEA2000 bus via a converter (Furuno IF-NMEA2K2). A NMEA sniffer shows that it forwards the input GGA and RMC sentences to its own 0183 output wires. The converter is bi-directional, so GGA & RMC are converted back to GNSS, COG/SOG, etc. The forwarded 2000 PGNs contain zero and n/a for those fields that do not exist in GGA & RMC (e.g. UTC offset, MVAR source & date, COG/SOG mag/true reference, etc.). This can confuse other devices on the 2000 bus.
ICOM support said there is no way to stop this forwarding. If other NMEA0183 devices do this, it could be causing problems whenever there is a mixture of 0183 and 2000 devices with a converter between them.
---rick