as always looking to the same lines of code i didn't catch my own fault ..
pff just changed the </p><p> in the second line in wanted <br>:

$txt =~ s{(?<=[\w&;\\\-:\/])$nl\s*$nl(?=\s*[\w&;\\\-:\/])}{</p><p>}g 
        if ( defined $nl );
$txt =~ s{(?<=[\w&;\\\-:\/])$nl(?=\s*[\w&;\\\-:\/])}{</p><p>}g    
        if ( defined $nl );
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cms does now linebreaks as assumed and wanted :))
"grand merci" to everybody for their interesting input maksl