### Please describe the problem.
addurl results in a different file than wget. Looks like git-annex is either decompressing it or triggering the server to serve it decompressed. This only happens with this one file in my usage, the other 32 .tar.gz that are added at the same time md5sum correctly.

### What steps will reproduce the problem?
    $ git annex addurl http://www.greenwoodsoftware.com/less/less-530.tar.gz
    $ wget http://www.greenwoodsoftware.com/less/less-530.tar.gz
    $ md5sum *

### What version of git-annex are you using? On what operating system?
* git-annex version: 6.20180509-g0632c49c22
* Arch Linux

### Please provide any additional information below.

[[!format sh """
$ git annex init
init  ok
(recording state in git...)
$ git annex addurl http://www.greenwoodsoftware.com/less/less-530.tar.gz
addurl http://www.greenwoodsoftware.com/less/less-530.tar.gz 

(to www.greenwoodsoftware.com_less_less_530.tar.gz) ok
(recording state in git...)
$ wget http://www.greenwoodsoftware.com/less/less-530.tar.gz
--2018-05-16 22:10:19--  http://www.greenwoodsoftware.com/less/less-530.tar.gz
Resolving www.greenwoodsoftware.com (www.greenwoodsoftware.com)... 104.200.21.227
Connecting to www.greenwoodsoftware.com (www.greenwoodsoftware.com)|104.200.21.227|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 339723 (332K) [application/x-gzip]
Saving to: ‘less-530.tar.gz’

less-530.tar.gz               100%[==============================================>] 331.76K   573KB/s    in 0.6s    

2018-05-16 22:10:20 (573 KB/s) - ‘less-530.tar.gz’ saved [339723/339723]

$ md5sum *
6a39bccf420c946b0fd7ffc64961315b  less-530.tar.gz
3d8def818aa59f10218e2549dc16f6b1  www.greenwoodsoftware.com_less_less_530.tar.gz
$ file -L *
less-530.tar.gz:                                gzip compressed data, last modified: Tue Dec  5 22:56:50 2017, from Unix
www.greenwoodsoftware.com_less_less_530.tar.gz: POSIX tar archive (GNU)
$ du -L *
332     less-530.tar.gz
1272    www.greenwoodsoftware.com_less_less_530.tar.gz
"""]]

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)
Of course! Still love git-annex to bits <3

> [[fixed|done]] --[[Joey]]
