>>>>I thought I'd posted something after this but anyway:
>>>>
>>>>I tested using both positive and negative priority and your directive always ran first. I *did* get it to work by changing your formatter to:

>>>>                    function bind() {
>>>>                        return ngModel.$formatters.unshift(function (value) {
>>>>                            return format(value);
>>>>                        });
>>>>                    }

Don't know why the priority approach didn't work but this shows that your formatter needs to be first in the $formatters array.....
>>>
>>>Wow, thanks for the clever solution, Viv. Seems like that error is gone although I'll do more tests.
>>
>>It's OK in this case since you always want your formatter to run after the angular one - but if you ever want to add another formatter after it then you are back to square one - i.e. needing to control the order of the relevant directives.
>>
>>Wish I knew why setting priority doesn't seem to work :-{
>
>Could it be a bug?

Think I worked it out:

The link function needs to be run pre-link with a priority > 0. i.e:

app.directive('smNumberFormat', ['$filter', function ($filter) {
            return {
                restrict: 'A', // only activate on element attribute
                require: '?ngModel', // get a hold of NgModelController
                priority:  100,
                link: {
                    pre: function (scope, element, attrs, ngModel) {
                    if (!ngModel) return; // do nothing if no ng-model

                    //Set the default decimal place to zero, if accuracy is not specified
                    var accuracy = parseInt(attrs.accuracy) || 0;
                    var stripCommas = attrs.stripCommas || true;

                    ngModel.$render = function () {
                        return element.val(ngModel.$viewValue);
                    };

                    var format = function (newValue) {
                        console.log("Running snNumberFormat formatter");
                        if (accuracy > 0) {
                            newValue = parseFloat(newValue);
                        } else {
                            newValue = parseInt(newValue);
                        }

                        //Let's not show any value if it's zero or not a number, so the placeholder text is displayed instead
                        if (isNaN(newValue)) return undefined;

                        newValue = $filter('number')(newValue, accuracy);

                        if (stripCommas) {
                            newValue = newValue.split(",").join("");
                        }
                        return newValue;
                    };

                      function bind() {
                          return ngModel.$formatters.push(function (value) {
                            return format(value);
                        });
                    }

                    bind();

                    element.on('blur', function () {
                        return element.val(format(ngModel.$viewValue));
                    });
                }}

BTW, would you agree that for numberInput we probably don't need to check for actual number, we may just check for the value (could be a string) being a number. If that code would have checked that instead of isNumber function, then I would not have a problem.

Not sure what you mean. If you're using 'type="number"' then angular ensures that the value received by your formatter will be the string value of a valid number.
If you're not using 'type="number"' then (assuming the model value is a number) then you will receive a number.