Strange behaviour of .length on a li set

I'm trying to play with sortable, but i'm experiencing a strange thing on this http://www.bamers.net/editor/editor4.htm.

I have 3 <li> with class="layers" and a progressive id.

If i call

var len = $("li.layers").length;

it gives len=4, while it should be 3.

So if a use

$("li.layers").each(function(i){
 ......
});

it loops 4 times, and not 3.

I can't explain myself if it's an errore of mine or some sort of bug.