I’ve found out that Safari can’t handle the same animated gif as background for multiple elements, it will just animate one of them at the same time. On a project I’m currently working on my I use the following trick to make all requests to the background image (in this case indicator_black.gif) unique.

[...]<br />
var text = transport.responseText;<br />
if (Browser.WebKit) {<br />
	text = text.gsub('indicator_black.gif', function(match) {<br />
		return match + '?' + new Date().valueOf() +<br />
		  Math.round(Math.random() * 5000);<br />
	});<br />
}<br />
[...]

Note that it uses Prototype JavaScript framework and you should too.