GWTTestCase session no longer working?

Question

We have a number of unit tests using GWTTestCase that have the structure of:

1) Make a request to login.

2) In the response handler, make second call that requires a login.

This all used to work fine, but after upgrading from 2.5.1 to 2.7.0, the tests fail with 'login required' errors. It appears that the problem is that the session no longer persists between the calls (lost or not connected). In particular, we have verified that the login call works, sets the session properly.

There's another test that updates session data for localization selection that fails as well with the same pattern.

Simplified code snippet:

userService.login("user", "password", new AsyncFail<DatumResponse<User>>() {
        @Override
        public void onSuccess(DatumResponse<User> result) {
            final int userId = 1053;
            final int userDocId = 44;
            authService.isAuthorized(userId, OPERATION_READ, userDocId,
                  new AsyncFail<AuthorizationResponse>() {
                @Override
                public void onSuccess(AuthorizationResponse result) {
                    assertFalse("Unexpected error.", result.isError());
                }
            }
        }
}

We were able to address this partially by adding the following to the test suite:

SecurityContextHolder.setStrategyName(SecurityContextHolder.MODE_GLOBAL);

This may indicate it's related to threads?

I understand that GWTTestCase is generally not the preferred method for testing anymore; this is an existing body of tests. "Use Selenium" or other suggestions are not really helpful.