mysterious text resizing when category listing appears

I have an odd problem right now with how a WordPress site I’m working on displays in IE (it displays fine in Firefox). I have a navigation bar set up in my header with this code:

<div id="header">
<div id="headerimg"></div>
<!-- BEGIN navigation bar -->
<table border="0" cellpadding="0" cellspacing="0" width="715" align="center">
<tr class="navbar"><td width="198"></td><td width="118"><a href="/main/" class="navbar">MAIN</a></td><td width="118"><a href="/category/events/" class="navbar">EVENTS</a></td><td width="128"><a href="/about-the-chefs/" class="navbar">THE CHEFS</a></td><td width="124"><a href="/private-flirting/" class="navbar">PRIVATE FLIRTING</a></td></tr>
</table>
<!-- END navigation bar -->
</div>

Everything works fine, EXCEPT when clicking on the Events category link. When I do that, the text size in the naviagation bar changes dramatically – it gets much larger and as a result, the navigation bar doubles in size.

But I can’t figure out why this is happening. My events category page (I have created a page called “category-3.php” for this) displays exactly the same way as, say, index.php. And there is nothing in my header.php that instructs WordPress to use a different style when displaying a category listing. I have also scoured my stylesheet and there is nothing there, that I can find, that instructs the stylesheet to format text differently when a category is showing. In fact, I explicitly state how the text is supposed to look in the navbar:

a.navbar {
font-size: 1.3em;
color: white;
}

a.navbar:hover {
text-decoration: none;
color: black;
}

To make matters worse, this problem only exists in Internet Explorer, it doesn’t happen with Firefox.

Anyone have any suggestions for how to proceed?