I’m looking for such an option too.
Okay. I figured out the solution. I have to switch en_GB to en_US
Okay. I think I found the reason.
My SEO-Plugin blocks Permalinks and other ways to transform the umlauts.
I hope this insight will help you in the future.
Yes of cause. I created a new post while the plugin was activated.
I just created another demo-post: http://www.fotocommunity.de/developer/uncategorized/ubertoller-test-weil-wegen-permalauts