We were having a problem cutting off text after <!--more-->. After examining the code and our content, I realized that the word more was in the content and the plugin was picking it up instead of <!--more-->. My solution was easy, go to line 111 of wp-members-core.php and replace 111 and 112 with the following:
$len = strpos($content, 'id="more'); echo "<p>".substr($content, 0, $len-6)."</p>";
So now it will search of the tag that wordpress creates for the more link. Just thought I would share in case anyone else is having a similar issue.