Well I'm an idiot - the fulltext index on page_text was missing from a default installation. It didn't break searches but probably slowed them down tremendously. Also set engine to MyISAM on page_text to avoid cryptic error messages from MySQL.
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>{$lang_insert_advhr_desc}</title>
<script language="javascript" type="text/javascript" src="../../tiny_mce_popup.js"></script>
<script language="javascript" type="text/javascript" src="jscripts/rule.js"></script>
<script language="javascript" type="text/javascript" src="../../utils/mctabs.js"></script>
<link href="css/advhr.css" rel="stylesheet" type="text/css" />
<base target="_self" />
</head>
<body onload="tinyMCEPopup.executeOnLoad('init();');">
<form onsubmit="insertHR();return false;" action="#">
<div class="tabs">
<ul>
<li id="general_tab" class="current"><span><a href="javascript:mcTabs.displayTab('general_tab','general_panel');" onmousedown="return false;">{$lang_insert_advhr_desc}</a></span></li>
</ul>
</div>
<div class="panel_wrapper">
<div id="general_panel" class="panel current">
<table border="0" cellpadding="4" cellspacing="0">
<tr>
<td><label for="width">{$lang_insert_advhr_width}</label></td>
<td nowrap="nowrap">
<input id="width" name="width" type="text" value="" />
<select name="width2" id="width2">
<option value="">px</option>
<option value="%">%</option>
</select>
</td>
</tr>
<tr>
<td><label for="size">{$lang_insert_advhr_size}</label></td>
<td><select id="size" name="size">
<option value="">Normal</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
</select></td>
</tr>
<tr>
<td><label for="noshade">{$lang_insert_advhr_noshade}</label></td>
<td><input type="checkbox" name="noshade" id="noshade" class="radio" /></td>
</tr>
</table>
</div>
</div>
<div class="mceActionPanel">
<div style="float: left">
<input type="button" id="insert" name="insert" value="{$lang_insert}" onclick="insertHR();" />
</div>
<div style="float: right">
<input type="button" id="cancel" name="cancel" value="{$lang_cancel}" onclick="tinyMCEPopup.close();" />
</div>
</div>
</form>
</body>
</html>