Why the animationend would be triggered in another srcElement?

Question

I make a function to handle css3 animate:

function play( $elm, animateClasss ) {
    $elm.addClass( animateClasss ).one(
        'webkitAnimationEnd animationend',
        function( evt ) {
            if ( evt.target === $elm.get(0) ) {
                // here is the right target elment
            }
            else {
                // here, the evt.target sometimes will be another elment which is like:
                // '<div class="anotherAnimateClasss"></div>'
                // .anotherAnimateClasss not use the `play` function
            }
        }
    );
}

For example, when I use play($('#a'), 'fadeIn') and handle another element '' by use $('.b').addClass('fadeOut'), these two ways could make the $('#a') trigger chaos, sometime triggers fadeIn, sometime triggers fadeOut.

Last, what I want to known is that: I addEvent on $elm, but why the callback sometimes triggered in another element?