Enforcing the maxlength attribute on mobile browsers

Try this one:

var $input = $('input')
$input.keyup(function(e) {
    var max = 5;
    if ($input.val().length > max) {
        $input.val($input.val().substr(0, max));
    }
});

jsFiddle here: http://jsfiddle.net/fttk2/1/

This problem is because predictive text is enabled on your keyboard, disable it and try again