xauth can't create .Xauthority file in homedir

Issue

• The homedir is autocreated and automounted from NFS by oddjob-mkhomedir and autofs.
• Logging in with e.g. ssh works correctly.
• Logging in with X-forwarding (ssh -X) fails with the following message:

/usr/bin/xauth:  error in locking authority file /net/example.com/mnt/gluster/vol01/homes/testuser/.Xauthority

• There is a .Xauthority-c created in the homedir with the correct ownership, but no permissions at all and with a date of februari 1970.
• If the whole homedir is deleted, everything is recreated correctly again except the .Xauthority file.
• The homedir resides on a glusterfs volume which is exported by an NFS V4 cluster resource.
• Autofs automounts the homedir via NFS.
• The permissions and ownership on the homedir are correct. No SELinux denials are added to the audit.log.