When a set of items have been routed, the Update Routing List button is used to clear the routed items. Occasionally, one or two items in the list will continue to be retrieved in the next search for items to route, even though the Route Date field has been cleared (I confirmed that there is nothing in the Route Date field). The only fix I have found is to reload the Serials textbase. This is in verson 7.

Has anyone else encountered this? It seems like a 'flag' has been set somewhere that is inaccessible to the user.

Yes, I have encountered this also, and have not been able to figure out why (especially as it is not consistent). However, it is not necessary to reload the textbase: try doing a rebuild of the Route Date field index. That works for me--and it takes only a couple of seconds (as long as nobody else is in the textbase).