Blackberry automatically accepting Meeting Invites

All of our Blackberrys (various models) are automatically accepting
Meeting Invitations. An invite is delivered to the handheld and is
automatically entered into the user’s calendar. It is automatically
“Accepted Tentatively”. This happens even if the invite is left unread by
the user. This is causing us big problems. Is there a way this can be
turned off? I’ve checked everywhere, on our BES server, and all the
settings on the Blackberrys themselves.

Sincerely,

Melan