What you are experiencing can be corrected by setting forcearray => 1 with XMLin(). I threw together a quick example which will demonstrate the differences. (Your sample XML file is in.xml.)
One other thing I have found to be helpful when working with XML::Simple is Data::Dumper.
#-- Sample code
print "Without forcearray...\n";
$mXML = XMLin('./in.xml');
print "With forcearray...\n";
$mXML = XMLin('./in.xml',forcearray => 1);