[jQuery] addClass on Safari within a click handler not working

[jQuery] addClass on Safari within a click handler not working

<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">Firstly thank you for jQuery - I'm loving it.
I have an interesting situation where if I add a class within a click event handler then the class does not get added. However if I add the same class as part of my regular $(document).ready handling then all is well.
To compound the problem, Safari 3.2.1 on Mac OS X exhibits the bad behaviour but Firefox 3.0.9 on Mac OS X honours the class being added.
Here's the code that does not work on Safari, but is ok on FF:</span><div><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">
</span><span class="Apple-style-span" style="white-space: pre-wrap; "><font class="Apple-style-span" face="Monaco" size="2"><span class="Apple-style-span" style="font-size: 10px;"> var resultFieldset = $("#results fieldset");

$("#visualise").click(function() {
resultFieldset.addClass("progress");
});
</span></font></span><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">
</span></div><div><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">Interestingly, executing hasClass("progress") immediately after the addClass shows true on Safari even though the class appears not to be added (I've also inspected the element via Safari developer tools and indeed there is no class added).
</span></div><div><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">If I change the code to:
</span></div><div><span class="Apple-style-span" style="white-space: pre-wrap; "><font class="Apple-style-span" face="Monaco" size="2"><span class="Apple-style-span" style="font-size: 10px;"> var resultFieldset = $("#results fieldset");

resultFieldset.addClass("progress");
$("#visualise").click(function() {
resultFieldset.addClass("progress");
});
</span></font></span><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">
</span></div><div><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">...then Safari and FF show the class on the page being ready (as you'd expect).
</span></div><div><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">Any ideas why Safari is not working in the first instance?
</span></div><div><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">Kind regards, 
</span></div><div><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">Christopher
</span></div><div><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: pre-wrap; ">P.S. jquery-1.3.2.min.js</span></div></body></html>