Hi Abraham I have enabled Sign-In with Twitter for my app http://adodson.com/hello.js/demos/twitter.html Previous usage showed this checkbox did not affect the ability to login to thirdparty apps, unlike the feature suggests, but rather provide auto-logging, i.e. not have to re-grant the app on each login.
oauth_callback is applied when calling oauth/request_token as per OAuth 1.0a. In addition to this it applies the same
oauth_callbackto the 2nd leg when calling oauth/authenticate and oauth/authorize as per OAuth 1 spec, 6.2.1
oauth_callback: The Consumer MAY specify a URL the Service Provider will use to redirect the User back to the Consumer when Obtaining User Authorization is complete.
As i say, its no longer honouring the oauth_callback, which contains important state information for the app.