Preposterous slack values for non-root users

[lunasophia]

When I run btrfs f u on my two btrfs filesystems as a non-root user, the tool reports the slack as 16.00 EiB. This is clearly wrong, and appears to be an underflow of a 64 bit unsigned integer.

[kdave]

Do you have a running device delete at the time you run the command?

[lunasophia]

I do not, no. The filesystems are pretty much entirely idle. The only "unusual" thing about them is I converted them from ext4. I ran all the commands in the btrfs-convert manpage.