multipart/alternative mail in doc group (bug?)

[Stephen Berman <steve@ims.uni-stuttgart.de>]

(Using Gnus 5.10.2) When I have several multipart/alternative mails
saved in a Unix mail file, make a doc group out of it with G f and
then press <space> on the group to read the mail, what I see in the
summary buffer is this:

 . [  39: John Doe              ] <* alternative> Our New Address
 .     [  22: John Doe              ] <1 text>
 .     [   9: John Doe              ] <2 html>

all of which is just the first mail in the file; all other mails are
not seen and not accessible by Gnus (but are e.g. by mutt).  This only
happens if the first mail in the file is multipart/alternative; if the
first mail is not multipart but e.g. just text/plain and all the
following mails are multipart/alternative, Gnus displays all entries
correctly in the summary buffer.

Is there some variable I should be setting to prevent this
(gnus-inhibit-mime-unbuttonizing is not relevant) or something else I
should be doing when creating a doc group out of multipart/alternative
messages, or is this a bug?  I couldn't find anything helpful in the
manual or internet.

--Steve Berman