Help please .. cannot end patrol

[Harmor]

Hi guys, I got one heck of a problem in my campaign. I started in the asian fleet and got moved to Freemantle in Australia. From there my order was to patrol Jawa Sea .. so ofc I went there, sunk quite some ships and went back once the marker on the map turned from orange to grey. However, my patrol went south from there. Once I made it back to Freemantle, it wouldn't let me dock .. the menu popped up where you can click on "Dock in harbor" (I got the german version so it might be a little different in english), restock and cancel but ... the dock option is greyed out, I cannot dock in Freemantle and I double and triple checked if I perhaps overlooked a message to relocate but didn't (the only really special message I got during the patrol is that american bombers bombed Tokyo). Is this a bug and if so, is there a workaround or am I just missing something?