The problem is that the map still seems to propagate touch events to iscroll. Let's try to prevent this by stopPropagation();
Edit
Here is the working jQuery mobile fiddle
var map_canvas = $('#map_canvas')[0];
// "mousedown" should be "touchstart" on mobile device
$(map_canvas).bind('mousedown', function(e) {
e.stopPropagation();
});
A fiddle with plain javascript here.
var map_canvas = document.getElementById('map_canvas');
// "mousedown" should be "touchstart" on mobile device
map_canvas.addEventListener('mousedown', function(e) {
e.stopPropagation();
}, false);
P.S.
Find here The link to the stopPropagation docs, comes in very handy some times ;)