After a git annex copy --auto -t m3 I got this error:

(Recording state in git...)
error: unable to resolve reference refs/heads/git-annex: No such file or directory
fatal: Cannot lock the ref 'refs/heads/git-annex'.
git-annex: git [Param "update-ref",Param "refs/heads/git-annex",Param "d768b20f76ce40157214a713fb0ccb9cfc9134c2"] failed

I did a git annex sync m3 and got

[...]
push m3
Counting objects: 2976, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (2052/2052), done.
Writing objects: 100% (2379/2379), 392.33 KiB, done.
Total 2379 (delta 1652), reused 460 (delta 316)
Auto packing the repository for optimum performance.
error: bad ref for refs/heads/git-annex
error: bad ref for refs/heads/git-annex
error: bad ref for refs/heads/git-annex
To /media/m3/annex
87c82c5..06219eb  git-annex -> synced/git-annex
be7ff5e..6625634  master -> synced/master
ok

And then I ran the command git-annex was trying to run:

$ git update-ref refs/heads/git-annex d768b20f76ce40157214a713fb0ccb9cfc9134c2
error: Trying to write ref refs/heads/git-annex with nonexistent object d768b20f76ce40157214a713fb0ccb9cfc9134c2
fatal: Cannot update the ref 'refs/heads/git-annex'.

git fsck --full gives no errors.

What does this error mean? Should I be worried? Thanks.