Can delete the WSD port under Vista , but not for Win7

Hi , I got a problem like Under vista SP2 , I can delete my printer and his
WSD port by using the PnPXAssociation::delete and DeltePrinter immediately .
but under Win7 , I can't delete the WSD port , the method can delete the
printer icon and all expect for the port . And I got a temporary solution
that I add a WSD printer by the windows network exporer and then delete it ,
like this , the "2" WSD ports are deleted together . So I dont know if it's a
Win7's bug or what else ? Because I have the impression that under Vista , it
has appeared this problem .

Thank you