[xwiki-users] AJAX requests don't finish / 401 Error

Hello. In short: Ajax requests like loading the attachment section, showing the user list or autocompleting searches don't work in my wiki. I see only the loading bar/circle and nothing else happens. When watching with Firebug, I realise there are two identical requests each, both with "401: Forbidden". The weird thing is, that the finished/aborted request got a result, but the wiki doesn't show it. The double-request is due to (I think) the Kerberos SSO, since the common way to authenticate seems to be to submit a request without credentials first, waiting for a 401 and then requesting again, this time with credentials. Fun fact: if i right-click the url in Firebug and choose "open in new tab", i get the correct resultset. A screenshot of the Firebug console can be found here: http://i39.tinypic.com/2moxw6v.png My setup: Apache that authenticates via Kerberos (and AD), then transfers to tomcat where the user is logged into the xwiki 3.1.4 automatically (this works). The wiki worked fine when I used NTLM authentication (wich only authenticates once per session, not for each HTTP-request) Did anyone encounter similar problems and is able to help me with this? Also, feel free to ask if you need more information. Thilo