Frank,
I recommend porting the oacs-dav package to use tdav http://aolserver.cvs.sourceforge.net/viewvc/aolserver/tdav/ which has better client support. It has not been looked at in 12 years but maybe it will help?
Sorry I don't have any resources to look into a bug I know it has worked with some WebDAV clients a few years ago but I haven't used in quite a while.
