### Please describe the problem.
When exporting a treeish with a subdir to a dir special remote, it fails with the error: 
[[!format sh """
git annex export master:subdir --to exportdir

fatal: Path 'subdir:' does not exist (neither on disk nor in the index).
git-annex: unknown tree
"""]]

I tried other treeish variations such as :./subdir, master:subdir but it didn't work either.
What is very strange to me is the ':' appended at the end of the path in the error.
Any idea what is going on here ? 


### What steps will reproduce the problem?
[[!format sh """
mkdir annex
mv annex
git init annex
git annex init --version=6
touch a.txt
mkdir subdir
touch subdir/b.txt
git commit -m "initial commit"
mkdir ../exportdir
git annex initremote exportdir type=directory directory=../exportdir/ encryption=none exporttree=yes
git annex export master:subdir --to exportdir

fatal: Path 'subdir:' does not exist (neither on disk nor in the index).
git-annex: unknown tree
"""]]


### What version of git-annex are you using? On what operating system?
[[!format sh """
git annex version

git-annex version: 6.20171003
build flags: Assistant Webapp Pairing Testsuite S3(multipartupload)(storageclasses) WebDAV Inotify DBus DesktopNotify ConcurrentOutput TorrentParser MagicMime Feeds Quvi
dependency versions: aws-0.13.0 bloomfilter-2.0.1.0 cryptonite-0.10 DAV-1.2 feed-0.3.10.4 ghc-7.10.3 http-client-0.4.26.2 persistent-sqlite-2.2 torrent-10000.0.0 uuid-1.3.11 yesod-1.4.2
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 p2p S3 bup directory rsync web bittorrent webdav tahoe glacier ddar hook external
local repository version: 6
supported repository versions: 3 5 6
upgrade supported from repository versions: 0 1 2 3 4 5
operating system: linux x86_64
"""]]


### 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)
Yep, it has been a long time since I used it but I am back to see what I can do to manage my files properly :)

> [[done]] --[[Joey]]
