Per: http://fedoraproject.org/wiki/PackagingGuidelines?highlight=%28--vendor+fedora%29 desktop-file-install --vendor fedora --add-category X-Fedora should be used.
Just a heads up to lett you know I'm alive and aware of this and your other 2 gnumeric bugs. I currently don't have a lot of time and concider these rather low priority but I will get around to them eventually.
Of course, no problem. (-:
This has been fixed in gnumeric-1.6.1-1 which should show up on a mirror near you soon.