I was having some wonky stuff happening with the whole system rebooting on me. Turned out the 5v power to the mpu was a little low (~4.2v) and random signals were dipping low enough to trigger stuff.
Check 5v level on mpu and source (which I think was actually on the driver board... not directly from the power supply).
I cleaned and reseated both ends of those connectors and power popped back up to 4.8v... problem went away.