### Please describe the problem.

In my unlocked adjusted branch, I get a lot of errors during "git annex sync". It appears to work fine otherwise (the files actually get synced). Below is what I see on the terminal. The repository is otherwise clean (no local or remote changes).
This has started to happen around a month ago, though I cannot pinpoint the exact version. This is in the same repo you used to debug the disappearing files in direct mode recently (thanks a lot btw!).

### What version of git-annex are you using? On what operating system?

[[!format sh """
$ git annex version
git-annex version: 6.20161110-gd48f4ca
build flags: Assistant Webapp Pairing Testsuite S3(multipartupload)(storageclasses) WebDAV Inotify DBus DesktopNotify XMPP ConcurrentOutput TorrentParser MagicMime Feeds Quvi
key/value backends: SHA256E SHA256 SHA512E SHA512 SHA224E SHA224 SHA384E SHA384 SHA3_256E SHA3_256 SHA3_512E SHA3_512 SHA3_224E SHA3_224 SHA3_384E SHA3_384 SKEIN256E SKEIN256 SKEIN512E SKEIN512 SHA1E SHA1 MD5E MD5 WORM URL
remote types: git gcrypt S3 bup directory rsync web bittorrent webdav tahoe glacier ddar hook external
$ lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 8.6 (jessie)
Release:        8.6
Codename:       jessie
"""]]

### Please provide any additional information below.

[[!format sh """
$ git annex sync --content
commit
On branch adjusted/master(unlocked)
nothing to commit, working tree clean
ok
pull origin
remote: Counting objects: 113, done.
remote: Compressing objects: 100% (113/113), done.
remote: Total 113 (delta 112), reused 0 (delta 0)
Receiving objects: 100% (113/113), 7.16 KiB | 0 bytes/s, done.
Resolving deltas: 100% (112/112), completed with 112 local objects.
From /srv/annex/bilder
   97a4806..78cb4ef  git-annex  -> origin/git-annex
ok
(merging origin/git-annex into git-annex...)

git-annex: fd:25: commitBuffer: invalid argument (invalid character)
failed

git-annex: fd:25: commitBuffer: invalid argument (invalid character)
failed

[...]

git-annex: fd:25: commitBuffer: invalid argument (invalid character)
failed
git-annex: sync: 2653 failed
"""]]
