That’s odd. This should fix it however, changing the code I posted above to:
#header-section.header-6 #header {
transition: height 0.5s ease-in-out;
-moz-transition: height 0.5s ease-in-out;
-webkit-transition: height 0.5s ease-in-out;
-o-transition: height 0.5s ease-in-out;
}
– Ed