I still have the problem (with both styles). I was poking around and I noticed that the content of the addon info tab is wrapped in a table, where the other tabs (which work, by the way) are not.
Code:
<div class="infosection">
<!-- fileinfo -->
<table cellpadding="0" cellspacing="0" border="0" width="100%"><tr><td>
...
(tab content goes here)
...
</td></tr></table>
<!-- /fileinfo -->
</div>
Just as a guess, I removed the table from a local copy of an addon page, and things seemed to work, but I'll be honest and say that the last time I looked at HTML was like six years ago, so I'm more than a little rusty with it; I may be way off.