I don’t think the problem is because of the size of the touch area per se although that would contribute to missing the button with your finger.
The real issue I believe is touch (or possibly click?) events firing on the back button. I am experiencing this exact same behaviour and I initially thought it was because my pages contain long lists (load/render time related problem) but no it is almost definitely something to do with touch events either not firing or firing too many times or overlapping with click events with a 300ms delay?? All pure guess work!
EDIT: This might be contributing to the problem? $element.bind('click' Slow?