Install bt-plugin to see if the problem is with your N810 unit, gps chip or navigation software.
Old N770 work just fine with bt gps devices.
What you call fix is internal application run by bt gps device.
So you can easily find out if your bt gps device already got fix, identified by flashing a led.
So test your N810 against external bt gps device first to see everything works fine than switch to internal gps chip/gps software.

Darius