A quick look at the sources makes me think you might want to try adding a trailing slash to the $url.

There's some code in ->open() which makes sure there is a trailing slash (which you can also see in the debug output), and as the URL string is being used to index associated resources (like the credentials) via hash lookup, I suppose you're getting two independent resource objects...  Just an idea.

("Scalix User" is the login realm, btw, not the user:pass combo. The latter is empty for the URL with the trailing slash.)