df -a

[Clem Taylor]

On my system, the 6.9 coreutils df is reading from /etc/mtab which
isn't a symlink to /proc/mounts. /etc/mtab does not match
/proc/mounts.

/etc/mtab:
/dev/md0 / xfs rw 0 0
proc /proc proc rw 0 0
...

/proc/mounts:
rootfs / rootfs rw 0 0
/dev/root / xfs rw,sunit=512,swidth=1536,ikeep,noquota 0 0
/proc /proc proc rw 0 0

So whatever is writing /etc/mtab (mount?) is doing the root device translation.

                         --Clem