If you take a look here, upon loading the page you will notice a DIV at the top. It is labeled "content" with "content_container" wrapped around it and finally, "page" around that. Clicking the bottom left or right arrows reveals other DIVs with similar tags but are properly aligned vertically. My attempts to resolve this led me to inspect the first carousel element (at the top) which had a correct height of 100%. However, when the subsequent DIVs were inspected, they also showed a height of 100%, causing them to move to the top when unchecked. I suspect there might be another surrounding DIV preventing "page" from obtaining a height of 100% during initial page load. Beyond that, I'm completely puzzled.
You won't find the source code useful because with Tumblr themes, separate code is created for each post. Thus, viewing the source code from your perspective will not match what I see. Text and Quote posts are the only ones aligned vertically, so please focus on those. Below is the complete theme code in case there's an error hindering the loading of height:100%.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<!-- Created by roseanneconner, powered by Tumblr. -->
<title>Earl Larson</title>
<link rel="stylesheet" href="http://static.tumblr.com/ux4v5bf/Btelpy2ff/fortheweb.css"
type="text/css" charset="utf-8" />
<link rel="stylesheet" type="text/css" media="screen"
href="http://jquery.malsup.com/cycle/cycle.css" />
<style type="text/css">
html {
height: 100%;
}
body {
/* Remaining CSS Code */
</style>
<script type="text/javascript"
src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script>
<script type="text/javascript" src="http://malsup.github.com/chili-1.7.pack.js">
</script>
/* Additional JS Script Code */
</head>
<body>
<div class="nav">
/* Next and Previous Navigation Links */
</div>
<div class="holder">
<div id="s7" style="height:100%;">
{block:Posts}
/* Individually styled blocks for different types of posts */
{/block:Posts}
</div>
</div>
</body>
<script type="text/javascript">_popupControl();</script>
</html>