This is not surprising. A map with space and water terrain was intended to be impossible as per map scripting. The dock and space dock buttons are obviously exclusive to the appropriate map type. The game thinks its a space map, and as such will not allow you to make docks, because the button is not there for you to press.
The computer can still make docks because they're not limited by the user interphase.
You can get your own docks if you manually add them from the scenario editor.
Alternatively, you can take an islands random map game and add space terrain, then you can build docks! Just don't complain when it hits space and you cannot make any space docks
