### Please describe the problem.

docs say
GETURLS Key Prefix
Gets the recorded urls where a Key can be downloaded from. Only urls that start with the Prefix will be returned. The Prefix may be empty to get all urls. (git-annex replies one or more times with VALUE for each url. The final VALUE has an empty value, indicating the end of the url list.

but when I am trying with a prefix -- doesn't return any... expected that one which is present and returned if I don't provide any prefix

### What steps will reproduce the problem?

git clone git://github.com/yarikoptic/datalad -b nf-custom-remotes
cd datalad
# there are requirements in requirements.txt, which you might need to install... or just do on smaug
git checkout 5b9cfd5008151c515f8bccadf39451055ab61b4b  
DATALAD_LOGLEVEL=1 DATALAD_LOGTARGET=stderr tools/testing/make_test_repo archive r1

### What version of git-annex are you using? On what operating system?
5.20150302~nd80+1  now tried also with  5.20150318+yoh20150323+1~nd80+1  (ie snapshot from march 23) with the same success

### Please provide any additional information below.

[[!format sh """
# If you can, paste a complete transcript of the problem occurring here.
# If the problem is with the git-annex assistant, paste in .git/annex/daemon.log

2015-03-26 15:56:05,612 [Level 1] Sending 'GETURLS SHA256E-s4--181210f8f9c779c26da1d9b2075bde0127302ee0e3fca38c9a83f5b1dd8e5d3b.dat' (base.py:120)
2015-03-26 15:56:05,613 [Level 1] Received ['VALUE', 'dl+archive:SHA256E-s153--f378a42b6ff4d90091a7dfa37ebe1fe2fc5926eafd12cde1f2ba5fd1bcbf5e1e.tar.gz/d/test.dat'] (base.py:120)
2015-03-26 15:56:05,613 [Level 1] Received ['VALUE'] (base.py:120)


2015-03-26 15:57:37,389 [Level 1] Sending 'GETURLS SHA256E-s4--181210f8f9c779c26da1d9b2075bde0127302ee0e3fca38c9a83f5b1dd8e5d3b.dat dl+archive:' (base.py:120)
2015-03-26 15:57:37,391 [Level 1] Received ['VALUE'] (base.py:120)

# End of transcript or log.
"""]]