I think this is due to your unordered list <ul> below the gallery.
All elements of your web page (html, body, 'gallery' div, 'I1' iframe and the gallery itself) have been given heights of 100% so the gallery should fill the browser window (assuming there is no other content on the page).
However, there is an extra element on the page (the <ul>) which takes up height and Mobile Safari is having trouble rendering content which takes up more than 100% of the height of the browser window.
Either give your gallery a fixed pixel height or reduce its height to a smaller percentage and allocate the remainder (100% - gallery height %) to the <ul>.