Only on cellphone, when using the site with a computer works perfectly. The option not to hide when scrolling down is on and still on my phone doesn´t work the menu. I´ve been trying to figure out what can be causing this but I really don´t know, and wonder why on your phone works well. I´m using Chrome on my mobile, Android and Motorola.
Maybe some plugin or css conflicts? I removed (temporarily) all my custom css and that didn´t seemed to fix it.