On small screens (max-width: 600px) the admin bar doesn't stick to the top of the page, this is because at this breakpoint the admin bar switches from position: fixed to position: absolute and since the theme uses position: relative for the body the bar positions itself at the top of the body element not the html.
http://awesomescreenshot.com/00e29p8m85
I'm not sure why position relative is used on the body but I removed it on my installation and it works fine so far.