We are using sortvals on both member and memberUid. We have been seeing duplicate member/memberUid attributes on some objects that have been modified (as well as a lack of sorting on those attributes). It seemed that there was a correlation between modifies to objects that experienced deadlocks and the objects that had duplicate member/memberUid attributes on them. We put the seqmod overlay in place - and this reduced the number of occurrences of the issue but did not eliminate them.
If you are seeing corruption, and have found something that helps fix it, I suggest you file an ITS.
--Quanah -- Quanah Gibson-Mount Sr. Member of Technical Staff Zimbra, Inc A Division of VMware, Inc. -------------------- Zimbra :: the leader in open source messaging and collaboration