In the fix to the issue #12408 Django started explicitly ordering test cases in the test suite, so that all TransactionTestCases are run together. Because of the way they work they can leave the database in a random state. Ordering makes sure all other test cases are run before them.
There's a function in django.test.simple called reorder_suite which takes care of handling that, but currently djangotestrunner.XMLTestRunner is not using it. This causes behavioral mismatch between xmlrunner and stock django test runner.