Qu Wenruo on Tuesday posted patches to fix the "famous RAID5/6 scrub error" and he went on to explain the situation, "Unlike many of us(including myself) assumed, it's not a timed bomb buried deeply into the RAID5/6 code, but a race condition in scrub recovery code. The problem is not found because normal mirror based profiles aren't affected by the race, since they are independent with each other. Although this time the fix doesn't affect the scrub code much, it should warn us that current scrub code is really hard to maintain."
With that said, two patches across just under 200 lines of code is able to fix this issue. Details on the linux-btrfs list. Hopefully these patches will end up getting merged for the Linux 4.10 kernel.
Update: Pardon the confusion, it turns out Btrfs RAID 5/6 code is only partially fixed.