This is in ref to a post I saw on the main MC13 download thread.
Ya, reducing the buffer in MC13 fixed the problem. I had upped the buffer to reduce the possibility of playback dropouts. Increasing the buffer has been helpful with ASIO, I assumed it would be the same for WASAPI. I reduced the buffer back to 0.5 seconds and WASAPI exclusive mode worked again.
The devs are going to have to figure out a way to make sure that a higher buffer setting doesn't prevent WASAPI exclusive mode from working. Otherwise WASAPI is going to be a support issue and frustrating for people who try it.
I didn't know Foobar was cheating on their WASAPI. They're usually quite picky about things being correct for anything that might affect playback quality.