invalidFiles does not apply to scope from my directive.

[krptodr]

I have a directive, that I am calling Upload.upload on. My directive template is specifying that ngf-model-invalid="invalidFiles" here is my example:

scope.invalidFiles = [];
            scope.invalidFile=null;
            scope.$watch('invalidFile', function(invalidFile){
                if  (invalidFile) 
                    scope.invalidFiles.push(invalidFile);
            });

<div ngf-drop="selectFile(picFile)" ngf-model-invalid="invalidFile" ngf-select="selectFile(picFile)" type="file" ngf-multiple="false" ng-model="picFile" name="file" ng-attr-ngf-pattern="{{form.schema.pattern && form.schema.pattern.mimeType ? form.schema.pattern.mimeType : undefined }}" ng-attr-ngf-max-size="{{form.schema.maxSize && form.schema.maxSize.maximum ? form.schema.maxSize.maximum : undefined }}" ng-required="form.required" accept="{{form.schema.pattern && form.schema.pattern.mimeType}}" ng-model-options="form.ngModelOptions && { allowInvalid: true, debounce: 1000}" ngf-drag-over-class="dragover" class="drop-box dragAndDropDescription">       
    </div>

However, upon line L559 below, the scope contains the invalidFile, but my scope.$watch('invalidFile') is never called.

https://github.com/danialfarid/ng-file-upload/blob/d911c553d0c1be76276a3b50ad5e3e8345c91747/dist/ng-file-upload.js#L556-L561

if I were to run ng-file-upload directly from my controller, then my $scope.$watches work fine.

Any idea for a solution?