Assume that your search service application has multiple query components in Microsoft SharePoint Server 2010 or Search Server 2010. When you issue a query that contains an Order By clause on a managed property, the query does not return all results that should be returned.
To resolve this issue, apply the following hotfix packages:
2479788 Description of the SharePoint Foundation 2010 hotfix package (sts-x-none.msp): February 22, 2011
2479795 Description of the SharePoint Server 2010 hotfix package (osrchwfe-x-none.msp): February 22, 2011