Firstly check the PP Manual for REQUIRED Mtree settings for PaymentsPlus sounds like you have Mtree Template setting for Highlight featured listing set to NO  it should be Yes.

Failing that...

Savant2_Plugin_ahreflisting.php is one of the files modified for PP. Your site may be displaying what was originally written in the code.

Original Code:
# Featured Link?
        if ($show["featured"] <> false) {
            if ( $link->link_featured ) {
                $html .= '<sup class="featured">'.JText::_( 'Link featured' ).'</sup> ';
            }
        }

Modified Code:
# Featured Link?
        if ($show["featured"] <> false) {
            if ( $link->link_featured == 1 ) {
                $html .= '<sup class="featured">'.JText::_( 'LINK_FEATURED' ).'</sup> ';
            }
        }

Two things where changed for PP, one was the addition of an IF statement so it only shows when the value of link_featured = 1 Remember that PP uses the field link_featured to identify the different listing types. 1 = Featured 2 = Standard and 0 = Free

The second was to make the text editable via the language file.  The problem (or beauty) with the JText::_( '' ) function is that is all too easy for a developer to forget to update the language file with the definitions. Jtext will return what's between the commas if it can't find a matching definition.

The Definitions are found in Mtree's Language File
language > en-GB > en-GB.com_mtree.ini