This bug has been reported upstream for 4 years now and nothing seems to happen on that front (and the last release is almost 3 years old). fedora already carries a patch for including "Unity" as a valid value, so please consider adding "Pantheon" to this list, too (for f22+ would be optimal).
This bug appears to have been reported against 'rawhide' during the Fedora 25 development cycle. Changing version to '25'.
There's an upstream commit for this that can be backported since August: https://cgit.freedesktop.org/xdg/desktop-file-utils/commit/?id=5b88c95c45e91781aed441c446210c6979350c3f
I'm applying this.
desktop-file-utils-0.23-2.fc25 has been submitted as an update to Fedora 25. https://bodhi.fedoraproject.org/updates/FEDORA-2016-d720054f2b
desktop-file-utils-0.23-2.fc24 has been submitted as an update to Fedora 24. https://bodhi.fedoraproject.org/updates/FEDORA-2016-9992b4e054
desktop-file-utils-0.23-2.fc24 has been pushed to the Fedora 24 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2016-9992b4e054
desktop-file-utils-0.23-2.fc25 has been pushed to the Fedora 25 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2016-d720054f2b
desktop-file-utils-0.23-2.fc25 has been pushed to the Fedora 25 stable repository. If problems still persist, please make note of it in this bug report.
desktop-file-utils-0.23-2.fc24 has been pushed to the Fedora 24 stable repository. If problems still persist, please make note of it in this bug report.