I have the same problem CORS problem automatically reset itself [Heroku hosted]
I figured out that the problem is in the Heroku DreamFactory image.
I moved my dreamfactory to DigitalOcean cloud hosting, the disadvantage of this move is that DigitalOcean is a paid service, but through there referral program they deposit for you $10 which is good for 2 month https://www.digitalocean.com/?refcode=4dd55fbff38b
I installed Dreamfactory by following instructions from this link http://ausago.com/2014/install-dreamfactory-in-digital-ocean-droplet/