OAuth 2.0 - Resource Owner Password Credentials Grant Fails

With two legged auth disabled on my account the following (replace with your own credentials) was working perfectly fine up until a few days ago :-

#!bash
curl -X POST -u "client_id:secret" \
      https://bitbucket.org/site/oauth2/access_token -d grant_type=password \
      -d username={username} -d password={password}

Something has changed and now it has stopped working and it always responds with