I updated to Firmware 6.70 on the DriveSmart 51 and 5.90 on the Drivesmart 50. not sure exactly when the extra FAT partitions were created. I only noticed them after I updated to latest City Navigator Map. I am using Win 10 to see these in both File Explorer and Control Panel's Storage, Drive Partitioning app.
No big deal, I was just curious about why the extra partition was made. I read somewhere that it was due to the new map file exceeding the 4GB but I don't see evidence of that anywhere.