[Bug-tar] Tar 1.26 sometimes fails with snapshot from 1.22

[goeran]

While investigating a problem I just reported about wrong inode
numbers in snapshot files, I also noted that tar 1.26 sometimes failed
to do backup when starting with a snapshot file from tar 1.22.  If the
problem is some kind of memory corruption, this might actually be the
same problem as the previous one.  But they appear quite differently
to me, so I thought I'd better submit both.

It seems as if tar 1.22 put an empty directory name in the snapshot
file for the root directory (/).  When tar 1.26 sees such a file, some
bug can be triggered, which causes it to backup almost nothing.  If I
manually add a / in the snapshot file as a file name for the root
directory record, the problem goes away.

It doesn't happen all the time though.  The smallest test case I've
managed to create looks like this:

   LANG=en_US.utf8 tar --create --listed-incremental=9.time --file=/dev/null 
--exclude-from=backup.exclude --verbose /

This command writes this output

    tar: /: Directory has been renamed from `'
    tar: /cgroup: Directory is new
    tar: Removing leading `//' from member names
    tar: Removing leading `/' from member names
    /
    /cgroup/
    /.readahead
    /.readahead_collect
    /]
    /bin
    /lib
    /lib64
    /sbin

And that is all.  Of course, there are many more files in my directory
tree than these.  (Like the "tar" command in /usr/bin! :-)

The snapshot files before and after the execution, as well as the
contents of the backup.exclude file, can be found at
ftp://ftp.uddeborg.se/pub/bug-tar-2

I'll be glad to help in any way I can to help debug this problem
(too).