On the page the page /oracle/apps/icx/por/req/webui/CheckoutSummaryPG there is a LOV about requester.
This field could be auto-filled through iProcurement Preferences with a value which don't match with the VO behind the LOV.
In this case, when I leave the page (clic on the "next" button), there is an error message : "Select a valid value".
I modified the VO in order to add some filters. The LOV works fine (I can't select value which don't match with my new VO) but if the auto-filled value matches with the standard VO and don't matches with my new filters, I don't have the error message.