Perl / XML::LibXML no parsing due to namespace

Question

I used XML::XPath to parse an xml-file and I encountered no problem. For several reason (not mantained (?), slowly, see for example here) I try XML::LibXML but don't succeed. The problem seems to be in the root of the xml-file. The following code does work:

use strict; 
use warnings;
use XML::LibXML;

my $prsr = XML::LibXML->new();
$prsr->keep_blanks(0);
my $xp = $prsr->parse_fh(\*DATA);

my @node_article = $xp->findnodes('/ARTICLE/*');

foreach my $node (@node_article) {
    print "$node\n\n";
}

__DATA__
  <ARTICLE xmlns:xsd="http://whatever" xmlns:xsi="http://whatever">
    <EVENT name="cat1" />  
    <EVENT name="cat2" />  
    <EVENT name="cat3" />  
    <EVENT name="cat4" />  
    <EVENT name="cat5" />  
  </ARTICLE>

But if the root contains the default namespace xmlns="http://whatever" the code above does not work (no output to terminal).

__DATA__
  <ARTICLE xmlns:xsd="http://whatever" xmlns:xsi="http://whatever" xmlns="http://whatever">
    <EVENT name="cat1" />  
    <EVENT name="cat2" />  
    <EVENT name="cat3" />  
    <EVENT name="cat4" />  
    <EVENT name="cat5" />  
  </ARTICLE>

One solution could be to delete (manually) the namespace but I want to avoid this since the original file will be downloaded and imported perdiodically. So, I have two questions:

1. Why the namespace does cause the problem using XML::LibXML but not when using XML::XPATH
2. How can I solve this problem using XML::LibXML?

Thanks for help.