[tracker2] nuvi 350 waypoint callsign plot errors

[n0rxd]

I have the OT2m, nuvi 350 and FMI cable, all working as advertised.  But 
occasionally, the nuvi plots a callsign with letter error (M0RXD), number error 
(N(RXD) or loses a letter (N0RX).  These plots stay in favorites until I delete 
them.  
For RX, I use unsquelched audio from the radio mic connector and selected 
software DCD in the OT2m.  I thought packets had a crc check that prevents such 
errors. Is there a setting or command (such as kantronics PASSALL) that I have 
set wrong?
Thanks,  Mark