It's the error reporting issues around closing and reopening files with outstanding buffered I/O that's really going to hurt us here. I'll be expanding my test case to cover that shortly.
Also, just to be clear, this is not in any way confined to xfs and/or lvm as I originally thought it might be.
Nor is ext3/ext4's errors=remount-ro protective. data_err=abort doesn't help either (so what does it do?).
What bewilders me is that running with data=journal doesn't seem to be safe either. WTF?
[26438.846111] EXT4-fs (dm-0): mounted filesystem with journalled data mode. Opts: errors=remount-ro,data_err=abort,data=journal