ember-cli --proxy works for GET but fails on PUT and POST

I'm trying to move my application from Ember Appkit to ember-cli and I'm having trouble replicating the proxy functionality previously provided by the APIMethod and proxyURL methods. I'm starting the server to proxy to localhost:3000 `ember serve --proxy http://localhost:3000/` This will read my data from the rails server correctly. However, when I try to write to the server, I get an error message `POST http://localhost:4200/api/v1/posts 408 (Request Time-out)` It's trying to post to port 4200, which is where the ember app is being served, but I want it to post to port 3000. How can I get it to do so? I'm using ember-cli 0.28, ember 1.5.1, ember-data 1.0.0-beta.7, and rails 4.1.