[rdiff-backup-users] Help - rdiff-backup removing permision on target folder

[bt101]

I'm been stumped by a problem for days.

I use nothing but linux and have been using rdiff-backup for years to backup 
all my machines to one central server.  I use the traditional method of the 
central server reaching out using ssh.

A friend wanted me to setup a backup of their windows machine to a linux server.
I tested this at home by making windows machine with cygwin on it.
It works just like my linux clients where the central backup server reaches out 
with ssh.
It works great.

I then setup a linux server and windows machine at the friends house.  As far 
as I can tell, the setup is (almost) identical to my test system at home.

I setup the linux server at the frien's house the same as my home system. I 
have a user called rbackup that performs the backup.  I pre-created the 
destination/target folder and made rbackup the owner.  When rdiff-backup runs 
for the first time, it does a complete backup successfully.  However, for some 
reason,when rdiff-backup is finished, it removes some permissions from the root 
of the destination folder.

The permissions change from:
drwxr-xr-x
to
drwx------

The next time rdiff-backup runs, it fails with many permission errors.
For example, it says permission denied for 
(rdiff-backup-data/mirror_metadata.2014-05-23T23:47:46-05:00.snapshot.gz).
The reason for this seems to be because (at some point in this second backup) 
rdiff-backup removed even more permissions from the root of the target folder.
They end up as:
d---------

Firstly, why is rdiff-backup making modifications to the root of the target 
folder?
Secondly, why does it do the most asenine thing that it can possibly do by 
removing all the permissions?

As a test, on the system with the problem, I tried to run a local backup.  That 
is, the central server makes an ssh connection to itself to run a backup.  This 
backup runs fine and does not modify the root of the target folder.

I gather I must have some difference between my test system (at home) which 
works, and this troublesome system, but I can't finger it out!

Any ideas?

Thanks.

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