How to properly specify context for Drupal behaviours
Just stop using context in this case.  I've been playing around with jQuery Masonry and I've not needed to use it.

(function ($){
  Drupal.behaviors.myModule ={
    attach: function(context, settings) {
      $('.view-SPECIFICVIEW .view-content').masonry({
        columnWidth : 300,
        gutterWidth : 20      
      })    
    }
  }
})(jQuery);


FYI, I'd also take a look at the Masonry recommendation to use the imagesLoaded plugin if there are images in your view.  It takes a LOT of future frustration out.