Opera Bug

[wheatus]

I have a page that will not display two list items in Opera but browses okay in IE6, Mozilla, Safari (Mac), IE 5.2 Mac.

url: http://www.hastings.ac.uk/switchon/whatisaCove.htm

The div in question is:
<ul id="greytabs">
line item classes: second and third

The UL is a nested div in #righttabs

CSS code is:

#righttabs{
position:absolute;
top:39px; left:432px;
background-image:url(../../switchon/images/navbar_r1_c8.gif);
background-repeat:no-repeat;
width:339px !important;
width:339px;
height:21px !important;
height:21px;
font:RussellSquare, Verdana, sans-serif;
font-size-adjust:none;
font-size:0.9em;
z-index:1;
}
ul#greytabs{
position:absolute;
margin:7px 0px 0px 57px;
padding:0px;
list-style: none;
font-family:RussellSquare, Verdana, sans-serif;
font-size:0.9em;
color:#000000;
}
ul#greytabs li{
float: left;
padding:0px;
margin:0px;
font-size:0.9em;
}
ul#greytabs li.first{
margin-right:80px;
color:#000000;

}
ul#greytabs li.second{
margin-right:65px;
color:#000000;

}
ul#greytabs li.third{
margin-right:0px;
color:#000000;

I have checked out various Opera sites but cannot seem to find the problem.

Any suggestions/useful links?