I've got a similar oddity at:
if you go to the 'meet the author' page, the right navigation div 'drops' (the content has a float:left on it).
oddly, all the subpages use the same layout HTML/CSS (it's a content management system). The only difference i can think of is this page's use of the unordered list. but i tried tightening up its margin, width, etc. but to no avail.
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