[Zope-dev] member properties disappear

Hi all, We develop a Website use Zope 2.4.3 and CMF 1.1. Today when I export the member's properties. I found some member's properties were disappeared. The reason I found is these member records stored in portal_memberdata were lose, but acl_users still has all portal user object( for example, there is a user named howard in portal acl_users, but no record id is howard stored in portal_memberdata ). I restored the yesterday's backup. Everything looks ok. Does anybody can tell me why? Thanks a lot Howard