Vespamarc you are a genius

I cannot thank you enough!
I did have an open streetmap installed on the satnav, once I deleted that it all started to work as it should do.
First let me apologize for the late reply, I was away on holiday struggling with a satnav that was very confused. The other issue I discovered whilst using it was that it did not recognize any of the way points it passed, I had to manually skip every one of them when I got there. Thankfully for this trip I was not the tour leader, just the backup.
Logically what it looks like happened is this: I installed a different map from OSM for the same country as the Garmin map (this was a test as I was planning on using OSM for other countries that my 390LM does not have installed). Everything behaved okay until I did a factory reset, at this point it looks like it enabled all the maps and that is when things got confused. I actually deleted the OSM file from the unit, not just un-selected it, though I am sure un-selecting would have been enough.
Thank you, this has saved me buying a new Garmin!