Any UNISIGNED8 value that is in excess of the maximum positive INTEGER8 value is deserialized as the maximum INTEGER8 value (9223372036854775807).

This was first witnessed by  when making a SOAPCALL to a Boca Roxie service that returned UNSIGNED8 values.

produced this simple ECL to illustrate the more generic issue:

OutRecord :=

    RECORD

        UNSIGNED8 id;

        string val{xpath('id')};

    END;

rec := FROMXML(OutRecord,'<Row><id>18196239629641154791</id></Row>');

OUTPUT(rec, NAMED('FromXML'), NOXPATH);

OUTPUT(PROJECT(DATASET(rec), TRANSFORM(OutRecord,SELF.id := (UNSIGNED8)LEFT.val; SELF := LEFT)), NAMED('proj'), NOXPATH);