Continuous button

HTML

<p>Clicking on the button, and holding the mouse button down will trigger the bug. See console for error log.</p>
<pre> el.is(':active') == $('*:active').filter(el).length > 0;
</pre> 
should always be true.

<button id='b'>Click me for bug</button>

JavaScript

var $el = $('#b');
function testActive() {
    // .is() doesn't use matchesSelector for active
    console.log("is: ", $el.is(':active') );
    // QSA is right
    console.log("$: ", $(":active").map(function() { return this.nodeName; }).get().join(" - ") );
}
var interval;
$el.mousedown(function( e ) {
    e.preventDefault();
    interval = setInterval( testActive, 100 );
});
$el.mouseup(function( e ) {
    e.preventDefault();
    clearInterval( interval );
});