outlook 2007 calendar events

my boss has outlook 2007 and recently had some calendar events "disappear" from outlook.
to troubleshoot I had him try logging to OWA, and the missing calendar event where there. So I think the problem was on the client, so I turned off "cache mode" in outlook and the events appeared again. but then later that day, they disappeared again.
He also said that the problem calendar events where invites that where sent to him, so they where not calendar events that he created.
so I'm trying to figure out the mechanics of invites sent to you. So if you have exchange server A, which is our exchange server, and exchange server B which is the exchange server that someone outside the company is using. And someone outside the company using exchange server B sends an invite, would the invite actually exist on exchange B?
if you accept the invite, is a copy stored on exchange A? also if the sender makes changes to the invite does exchange server B send something to A to inform the server of changes?
because of all of this, would that be why invites could appear to disappear?