Disappearing Guests

We've noticed that some of our elevated event guests have disappeared from the elevated event records, but we can't figure out at what's causing it.  I've tried to replicate it, but so far have been unable to do so.  We thought it might have something to do with paying off the event pledge, but again, no luck in replicating it.  I'd like to know if anyone has experienced anything like this, and if so, the cause and your solution.

I realize I'm not giving you much to go on, but this is a real mystery for us.

Thanks,

Chandra