Sliding the wrong amount in Safari and Chrome

I have an issue where the carousel moves the right amount on each click in Firefox and IE. However in Chrome and Safari, it doesn't appear to move along enough when the 'next' and 'previous' buttons are clicked.

I have noticed this is in jquery.jcarousel.js :

margin: function(e, p) {
if (!e)
return 0;

var el = e.jquery != undefined ? e[0] : e;

if (p == 'marginRight' && $.browser.safari) {
var old = {'display': 'block', 'float': 'none', 'width': 'auto'}, oWidth, oWidth2;

$.swap(el, old, function() { oWidth = el.offsetWidth; });

old['marginRight'] = 0;
$.swap(el, old, function() { oWidth2 = el.offsetWidth; });

return oWidth2 - oWidth;
}

return $jc.intval($.css(el, p));
},

So I am led to believe this is an issue with Safari/Chrome not 'reading' the margins set on the 'li' properly. Can anyone recommend how to get it moving the right amount in these browsers please?