I recently implemented the hide-preheader fix, but it appears to have the preheader indent in Outlook 2013...

<table class="em_wrapper" style="width: 560px;" border="0" cellspacing="0" cellpadding="0" align="center">
<td class="em_h_text" align="center" style="font-family: 'Open Sans', Arial, sans-serif; font-size: 1px; line-height: 1px; color: #a4d6eb; text-decoration: none;">
<div style="display: none; font-size: 1px; color: #333333; line-height: 1px; max-height: 0px; max-width: 0px-; opacity: 0; overflow: hidden;">We are currently backordered on the filters you ordered. Thank you for your patience.</div>

Any ideas?