Accepted meetings turning into Tentative meetings

I have a client that has two delegates that process his
meeting requests. When he receives updated meeting
requests for a recurring meeting one delegate accepts and
the other only views the invitation and stores the request
email for archiving, but does nothing else. When they
receive an updated request for a recurring meeting one of
them accepts and it updates correctly on the client's
calendar. At a later time when the other delegate views
the request in their inbox the client's calendar entry
turns from Accepted to a Tentative state. This situation
only occurs for recurring meeting requests sent from one
other specific client. Ideas or solutions? Thanks.