I also have seen the B2 on radar. Said fact was himhawed to them on freq. Said crew understood the inference and them, poof there was nothing to be seen. The aircraft was part of a flyby for an airshow. I talked to the crew later that day for the next days flyby. I asked them about it and was told it was for ATC purposes, should the TXPONDERs fail they still want the ability to be controlled via primary radar. I'm just a helo guy, so take it with a grain of salt.