It sounds like you are using the hoverIntent plugin. If that's true use .hoverIntent instead of .hover as event.
Fiddle: http://jsfiddle.net/HbjuW/
$(document).ready(function() {
$('#nav li').has('ul').hoverIntent({
over: function() {
$('ul', this).slideDown(250);
$(this).children('a:first').addClass("hov");
},
timeout: 500,
out: function() {
$('ul', this).slideUp(150);
$(this).children('a:first').removeClass("hov");
}
});
});