Richard please use switch -d and -v
rfpkg -d -v new-sources  and you will see the error

On Tue, Jun 21, 2016 at 5:16 PM, Richard Shaw <hobbes1069@gmail.com> wrote:
On Tue, Jun 21, 2016 at 11:06 AM, Sérgio Basto <serjux@gmail.com> wrote:
> Ok, upload-sources worked for me and I believe everything correct for a build.

are you sure ? 

Mine didn't show any errors:

$ rfpkg new-sources ~/rpmbuild/mythtv/SOURCES/mythtv-0.28.tar.gz
Uploading: /home/build/rpmbuild/mythtv/SOURCES/mythtv-0.28.tar.gz
######################################################################## 100.0%
Source upload succeeded. Don't forget to commit the sources file

and the sources file was updated properly. 

Thanks,
Richard