OK. Thank you for your analysis. I will try it. Many thanks.

Unfortunately, that's not possible. We are using DokuWiki in our Intranet. Access from outside isn't possible.

Sorry, I've forgotten to write that we are using IIS. You are right, DokuWiki and dokuwiki are separate folders – on UNIX systems. But using IIS on Windows Server, both names refer to the same directory. Therefore, we are able to use both styles. It works with all pages except pages using davcal.