Deleting all the objects help, though they always seem to jump back into the map maker as fast as you make any change to the heightmap, masks, textures, size etc.
This bug needs a fix ofcourse.
The exporting still exports the map correctly though if you remove all the objects, save the map, then exports. The maps comes out as they should atleast. But if you open up the map some other time in the map maker... It's back xD