Several Xsan admins are beginning to discover problems after installing Mac OS X 10.4.6 on Xsan 1.2. This Xsanity forum thread&sid=7002666a0fc7b4a63dc79655c02a78d1 is tracking the discussion. Please continue to direct comments to the thread as we track the issue.
Apple's Knowledge Base article 303549 describes the fix for Xsan 1.1 and earlier. Apparently the same fix can be applied to Xsan 1.2.
Kudos to MattG for the original post.