Byteman relies on TestNG tests either subclassing BMNGRunner or attaching BMNGListener as a test listener using the TestNG @Listeners annotation. Unfortunately, TestNG is remarkably stupid in how it handles the case where some classes in a suite attach a BMNGListener and others don't It decides that the listener should be used to run tests for all the classes in the suite.
This is utterly stupid but then again it is only one of many examples of idiocy in the design of TestNG whose control model is nothing short of incoherent.
I am not convinced BMUnit is going to be able to continue to support TestNG integration for much longer. However, at least for this current failing I believe I can implement a workaround in the Byteman integration class (just as I implemented a workaround for its equally idiotic test class setup/teardown behaviour).