jQuery speed test - sibling selector

I'll continue the previous post with a similar one. But this time I tested the sibling selector of jQuery. And as it turned out it is quite interesting but I don't want to kill the joke too early, so let's see that pic:

Well, IE is...slow, so to see things clearer I have removed it from the graph:

Obviously the fastest solution is: jQuery("h1 + h2")

BUT... there are some really interesting things going there. How can it be, that jQuery("h1").siblings("h2") is sooo much slower, than this:

jQuery("h2").filter(function () {
    return jQuery(this).prev()[0].tagName == "H1";
});


If anybody knows the answer, please share it with us!