Just discovered something:
When you edit your heightmap and import it into your world, be sure to reconnect your bridges to the roads. For some reason this causes them to disconnect.
EDIT: Just realized something.. I was plagued by lot tears before, but in the current version of the world there don't seem to be ANY lots tears at all. Maybe when you export your heightmap, then import it (Keep in mind the above warning), save and never edit the terrain again, lot tears disappear.
If this is true (Can people test it?), it's a step we should all follow at the very end of the development of our worlds.