Tab Jumping To Address Bar, Not Next Field After Select() [IE]

I am using select()/focus() to position the cursor at a particular field
on a form. This works, but when the user presses the Tab key in IE the
cursor jumps to the address bar rather than the next field (Firefox is
fine). Does anyone know why this might be happening and how to stop it?

Below is the code that I use to set the cursor position (it is somewhat
convoluted because it is generated via a series of macros). The cursor
is positioned correctly, but when I hit Tab the cursor does not follow
the expected flow through the page (i.e. it doesn't go to the next field).

// The page contains:
<script language="JavaScript1.2" type="text/javascript">
<!--
var focusId = 'fnameId'
SafeAddOnload(setFocus);
//-->
</script>
<input id="fnameId" type="text" size="50" name="fname" value="" />

// From a .js file loaded by the page:
// SafeAddOnload (used above) just delays execution until the
// page has loaded.
// getRef (used below) simply retrieves the DOM object using the id.
//
function setFocus()
{
obj = getRef(focusId);
if (obj != null)
try
{
obj.select();
}
catch (e)
{
obj.focus();
}
}