I've tested it and the "bug" is caused by the restriction of new harbors next to enemy borders. But in most cases you should be able to send a ship to this spot because it lays in your country, means it should not be affected but it is.
I've tested it and the "bug" is caused by the restriction of new harbors next to enemy borders. But in most cases you should be able to send a ship to this spot because it lays in your country, means it should not be affected but it is.