OK, I'm done with the preg_replace() in the paragraph parser. It's too buggy. Replaced with preg_match_all()/str_replace_once().
.mcePageBreak {display:block;border:0;width:100%;height:12px;border-top:1px dotted #ccc;margin-top:15px;background:#fff url(../img/pagebreak.gif) no-repeat center top;}