There is also LVM2 in the picture, but I'm not pointing any fingers. My gut feeling is this smells like some cache type thing waking up to sync/flush buffers and the pointer they follow lands them in the middle of some unwanted region.

https://en.wikipedia.org/wiki/Dm-cache

But I didn't see any evidence of caching in the BZ, so it's a potential redherring.

The data spanning the corrupted regions was an RSA key, which is fine... some folks might get their kackles up, but meh... I'm not sure why a key file would be cached, unless it's a read cache, and then the normal vfs cache would be where.