why does po goes to requires reapproval status when po line cancelled from po summary form

Hi ,

When a po line is cancelled from a PO form,  the  po status changed to require reapproval but when the line is  cancelled from PO summary line level  then the po status remain as approved only.

Is it because any changes in the PO form creates a revision and needed  approval. or there is some other reason.

kindly clarify.

Regards,

Kalyani.