i haven't had my gmail going to my bb for a while, but it did reconcile read/unread over BIS when I did and my other accounts reconcile over BIS just fine.
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~Di~
Windows 2003
Exchange 2003
BES 4.1
Are you sure? AFAIK reconciliation is one-way with BIS (Yahoo being an exception). You can always confirm by marking a read message as unread and choosing Reconcile Now.