Steps to Reproduce:
1.   mkdir /var/www/html/foo
2.   cp bar.rpm into foo
3.   createrepo /var/www/html/foo
4.   Run reposync

In my case, the actual command I used was:

/usr/bin/reposync -l -m -d --config=/var/www/cobbler/repo_mirror/test/.origin/test.repo --repoid=test --download_path=/var/www/cobbler/repo_mirror
/var/www/cobbler/repo_mirror/test/.origin

[mdehaan@mdehaan html]$ cat /var/www/cobbler/repo_mirror/test/.origin/test.repo 
[test]
name=test
baseurl=http://127.0.0.1/foo
enabled=1
priority=99
gpgcheck=0

The repo looks like:

#
[mdehaan@mdehaan html]$ tree /var/www/html/foo
/var/www/html/foo
|-- python-cheetah-2.2.0-1.fc10.i386.rpm
`-- repodata
   |-- filelists.xml.gz
    |-- other.xml.gz
    |-- primary.xml.gz
    `-- repomd.xml
  

The mirrored content from reposync is:

[mdehaan@mdehaan html]$ tree /var/www/cobbler/repo_mirror/test
/var/www/cobbler/repo_mirror/test
|-- config.repo (this came from cobbler, so disregard this one file)
`-- python-cheetah-2.2.0-1.fc10.i386.rpm


The output from the reposync command is:

[mdehaan@mdehaan html]$ sudo /usr/bin/reposync -l -m -d --config=/var/www/cobbler/repo_mirror/test/.origin/test.repo --repoid=test --download_path=/var/www/cobbler/repo_mirror
Unable to fetch metadata: requested datatype group not available
[test: 1     of 1     ] Skipping existing python-cheetah-2.2.0-1.fc10.i386.rpm


Actual results:

reposync only mirrored the rpm file itself, and did not create repodata on the remote end

Expected results:

reposync mirrors the xml files

Additional info:

We seem to think this is because the original source repo never had any group content.   Reposync should be mirroring the repo whether or not it has group content (because users often don't know anything about groups)

Removal of the -m from the command does not fix the problem.