error pushing stash ?

I have a git mirror remote setup on a few of my repositories:

[remote "backup"]
    url = /users/dbryson/backup/janus.git/
    fetch = +refs/heads/*:refs/remotes/origin/*
    receivepack = sudo -u dbryson git-receive-pack
    mirror = 1

I send my refs to the backup with:

$ git push backup

Only to find some odd error messages:

Counting objects: 133, done.
Compressing objects: 100% (109/109), done.
Writing objects: 100% (109/109), 31.25 KiB, done.
Total 109 (delta 82), reused 0 (delta 0)
error: refusing to create funny ref 'refs/stash' remotely
To /users/dbryson/backup/janus.git/
   549f8a4..8e93d51  8654 -> 8654
   ef6195b..549f8a4  origin/8654 -> origin/8654
 + 623e7cb...63d7262 origin/master -> origin/master (forced update)
 ! [remote rejected] refs/stash -> refs/stash (funny refname)
error: failed to push some refs to '/users/dbryson/backup/janus.git/'

Should I be concnerned about this or is it normal ? To be honest the fact that the stash isn't pushing doesn't bother me. But maybe it is a symptom of a larger problem ?

Dave