[xmlsec] why does xmlHasProp succeed but xmlUnsetProp fail? [SEC=UNCLASSIFIED]

[Cartland, Bruce]

// succeeds
a = xmlHasProp(node, BAD_CAST "id"); 
// also succeeds
a = xmlHasNsProp(node, BAD_CAST "id", BAD_CAST
"http://www.w3.org/XML/1998/namespace
<http://www.w3.org/XML/1998/namespace> "); 
// fails ???????
code = xmlUnsetProp(node, BAD_CAST "id"); 

 
?
thanks
 
Bruce  
PS. Apologies for the signature (auto-inserted by firewall).
 
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