OK, here's the simplest page which exhibits the behaviour. There are two columns floated left, each containing three content spots, which are all fixed width and height and set to overflow: hidden.
When content overflows either or both of the last two blocks by more than a couple of lines, the bottom two blocks are repeated on a new page and part of the overflowed text appears in them.
As an experiment I overflowed the text in the middle left block and nothing happens until the overflowed text is longer than the page height - or would be if it wasn't hidden. So the behaviour seems to be triggered by overflowing the page height.
Also when this happened, it pushed the right column to the next page, duplicated the overflowed block to the left column of the second page, followed by the bottom left block.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:svg="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:lang="en-nz" lang="en-nz">
<head>
<title>PDF source</title>
<link rel="stylesheet" type="text/css" media="print" href="print.css" />
</head>
<body>
<div id="container">
<div>
<div class="pagelayout">
<div class="zone Left">
<div class="spot s2">
<div class="element_image"><img src="/sites/all/files/s2-3.jpg" /></div>
</div>
<div class="spot s2">
<div class="element_text">
<h4>Size 2 block 1</h4>
<p>Size 2 block 1 article text.</p>
</div>
</div>
<div class="spot s4_tall">
<div class="element_text">
<h4>Size 4 block 3</h4>
<p>Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text. Size 4 block 3 article text.</p>
</div>
</div>
</div>
<div class="zone Right">
<div class="spot s4_tall">
<div class="element_text">
<h4>Size 4 block 2</h4>
<p>Size 4 block 2 article text.</p>
</div>
</div>
<div class="spot s2">
<div class="element_image"><img src="/sites/all/files/s2-1.png" /></div>
</div>
<div class="spot s2">
<div class="element_text">
<h4>Size 2 block 2</h4>
<p>Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. Size 2 block 2 article text. </p>
</div>
</div>
</div>
</div>
</div>
</div>
</body>
</html>
print.css/* Generic styles first */
p { color: black; }
h4 { color: black; font-weight: bold; }
/* Pages */
@page {
size: A4;
margin: 0;
marks: crop cross;
prince-bleed: 5mm;
}
.pagelayout {
position: relative; overflow: hidden;
width: 210mm; height: 297mm;
background: #F9F9F9; border: 1mm solid black;
}
.pagename { display: none; }
/* Zones */
.zone {
position: relative; overflow: hidden;
background: #CCC; border: 0.5mm solid #999;
}
.Header, .Footer, .Top, .Middle, .Bottom
{ clear: both; }
.Left, .Centre, .Right
{ width: auto; float: left; }
/* Spots */
.spot {
position: relative; overflow: hidden;
margin: 8mm 0 0 8mm;
background: white; border: 0.5mm dashed black;
}
.s2 { width: 90mm; height: 60mm; }
.s4_tall { width: 90mm; height: 127mm; }
.Header .spot, .Footer .spot, .Top .spot, .Middle .spot, .Bottom .spot
{ float: left; }
.element_text { background: #FFC; }
.element_image { background: #CFF; }
