Operations executing dnf as root do not appear to operate on the same cache/metadata as those executed as a regular user. for example:
$ dnf clean all
$ sudo dnf clean all
$ dnf check-update #metadata is refreshed
$ sudo dnf check-update #metadata is refreshed again
$ dnf --version
Installed: dnf-0:0.4.14-99.487.20140218git441c092.fc20.noarch at 2014-02-19 01:16
Built : at 2014-02-18 12:31
Installed: rpm-0:4.11.2-1.fc20.x86_64 at 2014-02-18 02:49
Built : Fedora Project at 2014-02-13 08:41
you should install dnf-plugins-core package that will install noroot plugin which will then check the root privileges.
Parag, your commend seems better suited for https://bugzilla.redhat.com/show_bug.cgi?id=1066747 :)
This works as expected but we didn't document it well. Upstream commit dfd08eb remedies this.
dnf-0.4.15-1.fc20 has been submitted as an update for Fedora 20.
dnf-0.4.15-1.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.