My guess is that it is something related the RAID handling in the block layer: I had a corruption on fat32 fs (/boot/efi partition) after upgrading grub-efi on my laptop. It sits on md-raid0 (intel fake raid)

I also had multiple corruptions of files written on ext4 patition but the /boot/efi corruption rules out ext4 bug.

EDIT: It was with 4.0.2 kernel on Debian