This is a “feature” not a problem. This is in fact the way Outlook is designed to work with delegates. In a Microsoft Outlook article I found some time ago it expressly said that this “feature” (problem) exists. When a delegate deletes the invite out of their inbox it will cause “changes” to be made and sent out if they were the meeting organizer or it will remove the meeting from the boss’s calendar if they received it from someone else. The intended recipient ONLY should accept or decline the invitation so it goes on the calendar or not. The delegate should NOT delete the invites from their inbox, but rather accept or decline on behalf of the mailbox owner if this is what is agreed upon. Now to fix this the mailbox owner, or boss, can go into the delegate properties and select NOT to send copies to the delegate, OR the delegate and boss can agree together never to delete invites from the inbox. Accept or decline, but do NOT delete. Users with multiple delegates increase their chances of problems since if any one of their delegates delete the invites from their inbox it will delete it from the mailbox owner’s calendar.