Do not use PartSet validator for Export feature. Local selection should be provided in the operation even when PartSet document is active.
<validator id="ExchangePlugin_ExportFormat" parameters="BREP|BRP:BREP,STEP|STP:STEP,IGES|IGS:IGES-5.1,IGES|IGS:IGES-5.3" />
</export_file_selector>
<multi_selector id="selection_list" tooltip="Select a set of objects" type_choice="Vertices Edges Faces Solids Objects">
- <validator id="GeomValidators_PartSet"/>
<validator id="GeomValidators_Finite"/>
</multi_selector>
</feature>