Richard, I'd suggest you view the lead activity of one of the leads that have an odd value for your lead status. Double click on the data value change activity and see if there's anything you can infer from there. If there is no campaign name next to the change, the change may be typed in by someone in your CRM. If your CRM tracks value changes for specific fields, turn that on so you can troubleshoot and find who the culprit is 🙂