[mkgmap-dev] Multipolygons and disappearing coastlines

Hi team, I have been asked by the Open Sea Map people to help them generate some maps with marine objects and while working on that I have noticed that if a way is part of a multipolygon then all its tags get removed. This is unfortunate because (in the test map I am looking at around Keil) the coastline is part of a multipolygon (some administrative boundary) and, therefore, the coastline doesn't appear in the map because its tags have been removed (or is it global warming?) So, is putting the coastline into a multipolygon a reasonable OSM thing? If so, should mkgmap be breaking the coastline by removing its tags? If not, how do we fix that? Any thoughts? Cheers, Mark