When an artifact is updated through SOAP the format is not taken into account and the value "1" is set in the database.
This cause issues when you try to export to XML an artifact that has been updated by SOAP since the retrieved value is not expected (not "text" or "html") so the XML validation fails. Consequently, this might also prevent artifact to be deleted since
story #11196 because Tuleap tries to save the artifact before the deletion when the plugin archivedeleteditems is present.