Globbing exclude fails with trailing slash

duplicity:
  Installed: 0.6.17-0ubuntu0ppa9~oneiric1
  Candidate: 0.6.17-0ubuntu0ppa9~oneiric1
  Version table:
 *** 0.6.17-0ubuntu0ppa9~oneiric1 0
        500 http://ppa.launchpad.net/duplicity-team/ppa/ubuntu/ oneiric/main i386 Packages
        100 /var/lib/dpkg/status
     0.6.15-0ubuntu2 0
        500 http://us.archive.ubuntu.com/ubuntu/ oneiric/main i386 Packages
python:
  Installed: 2.7.2-7ubuntu2
  Candidate: 2.7.2-7ubuntu2
  Version table:
 *** 2.7.2-7ubuntu2 0
        500 http://us.archive.ubuntu.com/ubuntu/ oneiric/main i386 Packages
        100 /var/lib/dpkg/status

I want to exclude, e.g.:

/home/me/.mozilla/firefox/profile.blah/Cache
/home/me/.mozilla/firefox/profile.blah/startupCache
/home/me/.mozilla/firefox/profile.blah/Cache.Trash

and all the files in them.

These two patterns work in an --exclude-globbing-filelist (the first pattern excludes all 3 paths, and the second pattern excludes the first path):

**/.mozilla/firefox/*/*Cache
**/.mozilla/firefox/*/*Cache/**

But this one fails to exclude files in /home/me/.mozilla/firefox/profile.blah/Cache:

**/.mozilla/firefox/*/*Cache/

Naturally, it should fail to exclude the 2nd and 3rd example paths, but it should still match the first one--but it doesn't.

As another example, another path to exclude is:

/home/me/.mozilla/firefox/profile.blah/Crash Reports/

This pattern works:

**/.mozilla/firefox/Crash Reports

But this one doesn't:

**/.mozilla/firefox/Crash Reports/

I don't see why the trailing slash should cause the exclusion of the path to fail.