Comment 8 for bug 1722376

All shipyards and the barbarian weaving mill have "needs_seafaring=true" in the the config file. Human player can build those only if allows_seafaring() is true.
Ports are treated different: They don´t have "needs_seafaring". So you can build a port on any port space you find, even if allows_seafaring() is false.

I think allows_seafaring() is true only if at least two port spaces exist. If there is only one, allows_seafaring() is false even though a port can be built.

So, AI needs the new rule that buildings with "needs_seafaring=true" may be built only if allows_seafaring()==true.
In my opinion, ports shouldn´t be prohibited on non-seafaring maps, since the human player is allowed to build them…