_filter_autop adds extraneous <br class="clear" /> to output

The _filter_autop function (which automatically converts newlines to paragraphs/brs) inserts a rogue <br class="clear" /> at the end of the text, which can mess up theme display and such when check_markup() is used. I looked through the function briefly but it ventures into Scary Regex Hell (tm) which is beyond my level of grasping just at the moment.