Unable to Signup as Parseuser, after failed signup call

I am using Parse.com for my android app.

• I have enabled ParseAnonymousUser

• I am getting the following error, when test with the following scenario

  ---> Turn off wifi, and try to signup

  ---> Then Turn wifi on, without killing the app, and then try to signup again. I get the the error: "java.lang.IllegalArgumentException: Cannot sign up a user that is already signing up." (error code: -1) ---> If i kill the app, then i successfully signup

Here is my signup code snippet:

        ParseUser user = ParseUser.getCurrentUser();
        user.setUsername(phoneNum);
        user.setPassword(phoneNum);
        mProgressDialog = new ProgressDialog(getActivity());
        mProgressDialog.show();
        user.signUpInBackground(new SignUpCallback() {
            @Override
            public void done(ParseException e) {
                if (getActivity() == null) {
                    return;
                }
                mProgressDialog.dismiss();
                handleSignupResponse(e, phoneNum, name);

            }
        });

Please tell me a solution asap. I have been struck here for a day.