createrepo multiple group files did not work

Hi,

I am running createrepo version 0.9.8 and yum version 3.2.29 on CentOS
6.2 where I created a private repository.

I have been baffled by following issues.

It works if I run only one group file "createrepo -g group1.xml
repo_directory". When I run second group file "createrepo -g
group2.xml repo_directory", the "yum grouplist" can only see group2,
not group1 any more. It seems that the later command "createrepo -g
group2.xml repo_directory" generated metadata overwriting and removing
the previous group1 metadata. Is it a bug or what I could do wrong?
Appreciate any helps to fix multiple group file metadata in
repository.

Thank you.

Kind regards,

Jupiter