characters not added in _rsync completion

[Wayne Davison <wayned@users.sourceforge.net>]

I've noticed something strange in the _rsync completion in 4.2.1 (I
tested both the debian packaged version of 4.2.1 and the latest CVS):
zsh sometimes fails to add all the common characters that it should
when completing an ambiguous option.  For example:

zsh -f
autoload -U compinit
compinit
rsync --bl<TAB>

The characters "ock" should be added (since the "--block" prefix is
common to both the listed completions), but nothing is added (the user
must either type more characters to remove the ambiguity, or cycle
through the matches with more TAB presses).

Other completions that fail to add common characters:

rsync --ch<TAB>    # should add "ecksum"
rsync --com<TAB>   # should add "p"
rsync --li<TAB>    # should add "nk"
rsync --no<TAB>    # should add "-"
rsync --par<TAB>   # should add "tial"
rsync --ti<TAB>    # should add "me"

(Note that two of those require a very recent rsync that has the
--checksum-seed and --partial-dir options, otherwise there would
be only one option to complete.)

However, most other options behave in the expected manner:

rsync --ba<TAB>    # adds "ckup"
rsync --del<TAB>   # adds "ete"
rsync --exc<TAB>   # adds "lude"
rsync --ig<TAB>    # adds "nore-"
rsync --inc<TAB>   # adds "lude"
rsync --v<TAB>     # adds "er"

Would anyone care to look into this?

..wayne..