Once, getting content from HTML::TreeBuilder , I had to find how to remove those   spaces appearing as spaces-that-are-not-spaces :) I tried :

my $tree = HTML::TreeBuilder->new_from_content( $m->content ) ;

for ($tree->look_down( _tag => 'td', class => 'obsTempText' ) )
{
    my $bla =  $_->as_trimmed_text ;
    $bla =~ s/ //g ;
    print $bla ;
}
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But the s/ //g did nothing. As marnanel said, the answer is to use HTML character entity references :

my $NBSP = HTML::Entities::decode_entities(' ');
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Then,

$bla =~ s/$NBSP//g ;
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removed the non-breaking spaces.