Try .stop()
Stop the currently-running animation on the matched elements.
Your code becomes
items.hover(function (e) {
$(e.currentTarget).unbind('mouseenter');
if ($(this).hasClass('xy')) {
$('div.block', this).addClass('xxx').removeClass('zzz').stop(true, true).animate({
top: '0'
});
}
}, function (e) {
if ($(this).hasClass('xy')) {
$('div.block', this).stop(true, true).animate({
top: topHeightVal
}, 200).addClass('zzz').removeClass('xxx');
}
});