If using a @media rule to mix targeted medias in a css file such as:

Code:
@media print
{
	.myGrid
	{
		font-size:18px;
	}
}

.someOtherClass
{
	font-size:12px;
}
Problem: updateRule will not work if an attempt is made to update the .myGrid rule:
since cacheStyleSheet assumes a flat structure:

Code:
cacheStyleSheet : function(ss){
       if(!rules){
           rules = {};
       }
       try{
           var ssRules = ss.cssRules || ss.rules;
           for(var j = ssRules.length-1; j >= 0; --j){
               // when it breaks, ssRules[j] will be a CSSMediaRule object, not a CSSStyleRule and CSSMediaRule doesn't have a selectorText property.
               rules[ssRules[j].selectorText.toLowerCase()] = ssRules[j];
           }
       }catch(e){}
   },
Definitely not a common use case but might still be worth noting