Deleting an instance of a recurring appointment

[Tim]

I've got a set of end-users who have several recurring appointments on their
Outlook calendars. When someone sends them a cancellation of a single
occurence of a recurring meeting, the entire series gets removed from their
calendars. The part of this that I find even more bizarre is that this
behavior is not consistent across the organization. Couldn't find any KB
articles for this, so I'm hoping someone here knows what might be causing
this and can let me know what I need to do to remedy this. Thanks in advace
for your help.