Testing REST server with several different clients only Guzzle (v3 and v4) give a different result.
When attempting to delete a ContentTypeGroup that doesn't exist should return 404 - If the content type does not exist which only Guzzle is returning a 200 OK (from the tested clients)
Firefox RESTClient addon
Guzzle 3 and Guzzle 4:
Guzzle4 request print_r
Guzzle4 response print_r