Bug 1031110

Apologies if this has been reported before.  I suspect that I'm not the first one to run into this but my searches didn't turn up anything.  Here goes:

Trying to upgrade from FC18 to FC20 fails with the following error:

<package downloads elided>
testing upgrade transaction
rpm transaction 100% [========================================================================================================================]

Upgrade test failed with the following problems:
insufficient disk space
  need 8M free on / (1.6G free)
fedup ERROR: Upgrade test failed.
rpm transaction 100% [========================================================================================================================]

The affected system indeed has 1.6G free:

# df -h
Filesystem               Size  Used Avail Use% Mounted on
devtmpfs                 2.0G     0  2.0G   0% /dev
tmpfs                    2.0G     0  2.0G   0% /dev/shm
tmpfs                    2.0G  2.3M  2.0G   1% /run
tmpfs                    2.0G     0  2.0G   0% /sys/fs/cgroup
/dev/mapper/fedora-root   20G   17G  1.6G  92% /
tmpfs                    2.0G  388K  2.0G   1% /tmp
/dev/sda1                477M  128M  320M  29% /boot

# yum --enablerepo=updates-testing install fedup
Loaded plugins: auto-update-debuginfo
Package fedup-0.7.3-4.fc18.noarch already installed and latest version
Nothing to do

It looks like either the free space check is off or fedup is telling me that 1.6G is not enough for an upgrade but reports the wrong number (e.g. that 8M is really 8G.)