### Please describe the problem.

git-annex dies of signal 11 when syncing content with Box.

I noticed that the assistant stopped syncing after a few files, so I tried to sync manually through the terminal and saw the error.

### What steps will reproduce the problem?

    $ git annex sync box.com --content
    commit  ok
    copy myfile1 (checking box.com...) (to box.com...) 
    ok                      
    copy myfile2 (checking box.com...) (to box.com...) 
    ok                      
    copy myfile3 (checking box.com...) (to box.com...) 
    ok                      
    copy myfile4 (checking box.com...) (to box.com...) 
    ok                      
    copy myfile5 (checking box.com...) error: git-annex died of signal 11

The number of files that are copied correctly is quite random, some times it syncs 200 files and other times only 2 or 3.


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

5.20141125 on Debian Sid (everything install from official packages)

### Please provide any additional information below.

I don't know how to get more details of the problem, I haven't manage to get a more precise error activating logs or verbose mode, if there's anything I can do to debug the problem I'll be more than willing.
