I see this in the ODWEK Java docs for 10.5.
NOTE: If the Application Group contains fields for which the value is not provided by this call -for example, 'Unique Id' or 'Hash SHA-256' fields - but rather generated on the server when the document is stored, the ODHit returned by this method will not contain the server generated values. In order to access those values, a new query should be performed.
I don't see that update in the 10.1 ODWEK Javadocs, but it applies to both versions.