Add a property to the class lStayPut = .F., set it in MUPDATEROWSOURCE method and check in VALID.

*MUPDATEROWSOURCE method
if this.yesno("Add new record/value to "+alltrim(lcAlias)+"list?")
  ...
  This.lStayPut = .F.    
else
  This.lStayPut = .T.    
endif

*VALID method
local llRetVal
llRetVal = This.Refresh(.t.)
if not llRetVal or This.lStayPut
	return 0
endif

< snip >