A similar bug has been recorded 11 months ago.

Looking at the source (and showing my findings...), I don't readily see what causes this behaviour. The relevant pieces of the code are:

use constant HAS_HTML_TIDY => do {
    local $@;
    eval { require HTML::Tidy; 1 } or do {
        unless ( eval { require XML::Clean; 1 } ) {
            die( "Please install HTML::Tidy (preferred) or XML::Clean 
+first" );
        }
        0; # Has XML::Clean but no HTML::Tidy
    };
};
...
sub parse_file {
    ...
    if (HAS_HTML_TIDY()) {
}
[download]

It seems to me that the use constant does somehow not have the effect of declaring HAS_HTML_TIDY, but I don't see how that happens.

Do you have HTML::Tidy installed? Also, as you seem to be running the system Perl, how did you install the module? Did you use your vendor's package manager?