You may also need to check Language and Locale on user Preferences on your browser (drop-down beside your name). In theory it shouldn't matter what date format is set on the physical server as you may have users accessing it from all over the world. It should really be the browser that matters. However! - you may want to check the regional / date-time settings on the physcial server - and on your own PC.
Language and locale is Norwegian on both the server and my PC.
On Tableau Server the Language is English and locale is Norwegian.
Reply from Tableau Support:
This is a known issue that will be resolved in our next maintenance release of Tableau Server, version 8.1.4.
Version 8.1.4 available today. :-D