This is happening because, the height of the header in your site is more than our Appdev demo site. The easy fix for this is to change the “offset” value in the main.js file (line number 118). In your case value should be -165 instead of -80.
I see that you have installed a plugin called “autorep” which is probably doing this when you click on the button. Please disable it and see whether this behavior occurs still. You can see that in the demo site we don’t see this behavior. Thanks!