On the GP1971F, "polylines" (aka many lines) are temporary markers, usually added or deleted as needed per any session, and generally not meant to be saved in the same way waypoints, routes and/or tracks are typically.
If you have an area you want to mark out (that's not already marked on the chart), try creating a route instead and re-naming it to something unique like Poly1, Poly2, etc. and back the route data up to an SD Card.
Hope this helps, :sail
- Maggy
