Recent update broke raid automount

[sirlark]

Hi all,

I recently updated my system, part of which included a bump of mdadm to from 3.2.3-r1 to 3.2.5, and a gentoo-sources bump from 3.3.4 to 3.4.0. Upon reboot into the new kernel, mdadm complains on boot that it can't get an exclusive lock on mapfile <hostname>:1

Where previously I have a single raid device (/dev/md127) I now have two devices (/dev/md126 and /dev/md127) which both lay mutually exclusive partial claim to the component partitions of my original raid. If I use mdadm -S to stop the two md12[67] devices, and assemble the raid manually, I can mount it just fine, so the raid drive itself is hunky dory.

So,

1) Why have I suddenly got this extra raid device /dev/md126, and how re those numbers assigned anyway
2) Where is this mapfile, and why can't it be locked during boot, and how can I make it lockable?
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[Jaglover]

There is a bug opened https://bugs.gentoo.org/show_bug.cgi?id=416081
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