Sorry about the lack of details, just wanted to send a quick report since you pushed 3.6b2 to PyPI so it will likely affect many others as well who just pip install coverage like I had been doing without a version guard.
I've been deploying from PyPI, so my code runs fine on 3.5.3. I haven't tried running under 3.6b1 (will try now). Basically, all my tests showed 0% coverage under 3.6b2.
It looks like it works fine under 3.6b1 but not 3.6b2.
Because I'm running coverage via several nose plugins (with are then run via django-nose), I don't have a lot of direct experience with coverage (sorry).
Find attached some coverage.xml files running the same tests under different version of coverage.