I think you are going to have to show us more of your surrounding code as there is nothing in the XML::DOM code that would suggest this behaviour and the minimal test case:

use XML::DOM;
                                                                      
+          
my $d = XML::DOM::Document->new('Test');
my $e = $d->createElement('Foo');
$e->setAttribute('foo',0);
$d->appendChild($e);
print $d->toString();
[download]

works fine here with 1.43 of the module.

/J\