Negative hashtags are an aspect of our product that we've introduced to manage content collection and make sure that you're pulling the most relevant content as possible.
So...why are they not working?
Just make sure that you've eliminated all spaces between commas and different keywords as this will effect which words or phrases that are being pulled. For example, if you include the a space i.e. 'chocolate, easter' it will pull the space in front of 'easter' and you will then still get photos tagged with the phrase 'easter' in your inbox.