If you can wrap your submenus under your main menu you can avoid this issue.
Html
<div class="slide">category:
<div class="slide_panel"> <a href="#" title="">asdf</a>
<br /> <a href="#" title="">qwerty</a>
<br />
</div>
</div>
<div class="slide">another category:
<div class="slide_panel"> <a href="#" title="">another asdf</a>
<br /> <a href="#" title="">another qwerty</a>
<br />
</div>
</div>
JS
$(".slide").on('mouseenter mouseleave', function () {
$(this).find(".slide_panel").stop().slideToggle();
});