I felt like exploring the server and took a ship into old port. As I was done exploring I was going back into the port, but there was a little obstacle in the way.
In other words, the first door in the sewers is unlocked when one is coming from the port's direction, but not vice versa. To me this seems like a clear bug that could be fixed.
Cheers.
Being able to pick locks worked for me.
For me it says "a specific key is required". I hope you mean the same door as I do.
I might be thinking of a different one! Actually, come to think of it I'm fairly sure I disconnected before leaving Old Port the same way I had come, so the door could have very easily been locked back up.