Hi Jennifer, we struggle with this too. It's actually our AE's that do it, so now I see our sales team's activities...not the lead. I don't know that I have a great solution - someone told me I'd just have to delete the lead and start over or try to get them to fill out a form to re-cookie, etc.
Sorry I can't be of more help. But I am subscribed so I can hear how others are dealing!
- Emily