Is there a problem with Microsoft using BSD code in their proprietary products? The developers clearly understood that was a potential outcome when they placed their code under a BSD license. As a result, they probably don't mind
That said, would it be nice to have seen MS contribute some code back? Yes, but that was not required by the license so there is no problem. That is the whole point of the BSD-style licenses: you can take my code and do whatever you want with it; you are under no further obligation to me.