I can confirm your symptom (i.e. "no error") when I force XML::Simple to use XML::Parser as its parser. Maybe your configuration uses XML::Parser as its default? Consult the "ENVIRONMENT" section in XML::Simple's documentation.
If I let XML::Simple use XML::SAX
as parser (which is my default, since it is installed), I get
Undeclared prefix: person at E:/perl/site/lib/XML/NamespaceSupport.pm
Which is "somewhat" similar to the message Anonymous Monk reports in the first reply in this thread (but who -- judging from his message -- uses some other parser).