So are you saying that if we use z4root and superuser is still there, we should delete superuser? or that z4root has simply failed and there's nothing we can do?
I haven't gotten this method to work any way I try it - updating before unrooting, updating after unrooting, anything. Since I used DoRootForWindows as the original root, is that why z4root won't work? Also, no, the phone never rebooted at all during the unroot/reroot process with z4root. Only by going back to DoRootForWin was I able to sucessfully re-root.
z4root did seem to partially unroot, as my wireless tether stopped working. But no reboot, update fail.