4 requests missing from list, but still show up in reports

Problem Description:
4 requests seemed to disappear over the past few days. Now, there's a difference between the number of requests listed on my main work order page (12) and the number of requests in my custom "Complete List of Requests" report (16). In other words, the missing requests still show up in reports, but not in the request list.

Notes:
I'm displaying all requests on the work order page. There's nothing obviously similar about the "invisible" requests (those that appear in reports, but are not showing up in the request list). New requests work fine.

Help?:
Has anyone seen this kind of behavior before? Is there a way to get rid of the "invisible" requests or, better yet, recover them?

Regards,
Rich