python - getattr throws TypeError on ImageSpecField -

class mymodel(models.model):     ...     original_image = models.imagefield(upload_to=upload_image_to)      thumbnail = imagespecfield(         processors=thumbnail_processors,         source='original_image',         format='png'     )     ...  obj = mymodel() val = getattr(obj, 'thumbnail') 

... gives me following error: "typeerror: can't pickle instancemethod objects"

django 1.7.1
imagekit 3.2.4