Line 56 of the plugin uses str_replace to generate the permalink, where a regular expression would be a better fit.
Consider a blog on example.com with an author login of exam and the display name of exam ple.
Using str_replace to generate the link changes the permalink from example.com/author/exam/ to exam-pleple.com/author/exam-ple/
Replacing line 56 with the code below fixes this problem
$patten = '/\/' . $author_nicename . '\/$/';
$replacement = '/' . $this->users[$author_nicename] . '/';
$link = preg_replace($patten,$replacement, $link);