Currently, if another process sets up an Offline Update, pk-offline-update may run first; if it does, it deletes the symlink, then fails to read the (missing) transaction file, then exits unsuccessfully, rebooting the system. This messes up the other process (e.g. dnf system-upgrade) pretty badly. As per the discussion here: http://lists.freedesktop.org/archives/systemd-devel/2015-July/033623.html the recommended behavior is to check to see if the update was prepared by this tool, and if not, exit quietly.
Patch sent upstream: https://github.com/hughsie/PackageKit/pull/78 This will require backporting to F22 and F21.
PackageKit-1.0.6-2.fc21 has been submitted as an update to Fedora 21. https://bodhi.fedoraproject.org/updates/FEDORA-2015-15440
PackageKit-1.0.6-2.fc21 has been pushed to the Fedora 21 testing repository. If problems still persist, please make note of it in this bug report.\nIf you want to test the update, you can install it with \n su -c 'yum --enablerepo=updates-testing update PackageKit'. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2015-15440
PackageKit-1.0.6-2.fc21 has been pushed to the Fedora 21 stable repository. If problems still persist, please make note of it in this bug report.