[mkgmap-dev] Etrex sea floods tile unless well zoomed out

I just noticed on my etrex that tiles that touch the coastline are flooded when zoomed in less than about 30Km. Neither mapsource or the nuvi show the same problem with the same map (this is with --generate-sea=polygons). When zoomed out, the coastline looks fine. Anyone else seen this? got a fix? Mark