If a new jQuery object is created with the usual syntax ($('div', document.body)), the constructor function doesn't get far before it realises that it needs to call the ''new'' keyword on itself, with this line:

	if ( window == this )
		return new jQuery(a,c);

However, as you can see, only the two formal parameters are passed into this second call -- that is, any extra arguments are discarded. This would not be a problem of course, except that later in the function there is a provision for an extra function that may be passed in:

	// See if an extra function was provided
	var fn = arguments[ arguments.length - 1 ];

	// If so, execute it in context
	if ( fn && typeof fn == "function" )
		this.each(fn);

By the time this code is reached, the extra un-named argument will have been discarded, whether or not it was present in the original call.

This bug could be circumvented if the original statement explicitly instantiated a new object (new jQuery('div', document.body, someFunction)) -- but since $(etc) is the conventional syntax, this feature is effectively unreachable by a normal jQuery call.