I generated and down loaded a set of Australia Garmin Navigable maps.
The problem occurs in a few suburbs on the north sydney harbour shore, and is that the map displayed on the Garmin has water south of a straight line from the tip of Watsons Bay to approximately Balls head. All north shors suburbs south of that line appear as water (Milsons Point, Kiribilli, Cliftons Gardens etc). The roads display correctly but that background is water.
When I looked at the map in the web it all looked fine.
I am getting the same thing in East London, South Africa around Esplanade Road which runs next to the shore.The only thing I have tried that I think might have made a difference was simplyfying as section of the coastline which is very detailed and looks like it is trying to trace every rock on the coastline. I only did it on a small section and it seemed to make a difference, I think. I am a bit nervous about making in major changes to the coastline as I am still quite new at this. I also got the map from garmin.openstreetmap.nl.
Do you know if this happened in earlier versions as well?
I think this has to do with removing the admin 9 and 10 levels prior to providing the data to Mkgmap, at some points admin nodes share coastline nodes (e.g. near Landenburg Place, just south of the Greenwich place node, left of Waverton).
I’m not sure if it’ll help, but you could try sourcing your maps for Australia from http://www.osmaustralia.org/
Of course if you’re not happy with that, you could always download an extract of australia, then run it through mkgmap to suit your liking