No bugs at all. Water units have already been in Military for a fair while. The AI plays true water units fine, but at the moment, there is a slight problem with docks. If the building unit is a land unit (as the worker would be), they cannot build the building in water, for some reason. Human controlled players can fine, but the AI can't seem to wrap its...er... artificial intelligence around building something on a different surface than the builder is on.