Push to patch queue repo fails

Attempt to push to queue repo fails with the following error:
{{{
abort: repository is unrelated
}}}
even though patch queue repo has no recorded changes.

After initial qclone patch queue repo in .hg/patches is empty as expected
(tip is -1:000000000000). Then I pull from existing patch queue repo. Then I'm trying to push and getting this error. qpush also fails, although error looks different:
{{

{\\ itkach@itkach-desktop:~/mwlib-patches/.hg/patches$ cd ../..\\ hg qpush https://bitbucket.org/itkach/mwlib-patches/\\ abort: patch https://bitbucket.org/itkach/mwlib-patches/ not in series\\ }}

}