gnus-read-mark not preserved

[Stephen Berman]

When I read newsgroup articles with Gnus they get marked with `R'
(gnus-read-mark) and are not displayed the next time I enter the
group.  However, I have been noticing that, when I

1. enter a group that satisfies gnus-large-newsgroup,
2. have Gnus fetch less than all the articles, 
3. read articles, exit the group, and at some point exit Emacs, 

then the next time I enter the group in a new Emacs session, the
articles I read the last time are displayed, i.e., not marked read.

I am not certain this happens every time and with every group, and I
am not certain, but I think, this does not happen when I fetch all
unread articles.  I have noticed this repeatedly with
gmane.emacs.pretest.bugs and gmane.emacs.devel (I have
gnus-select-method set to '(nntp "news.gmane.org"); those are the
groups for which conditions 1 and 2 above most often hold according to
my Gnus usage.

I am currently using GNU Emacs 22.1.1 (i686-pc-linux-gnu, GTK+ Version
2.10.6) of 2007-06-02 on escher, but I have noticed this for some time
on CVS builds, though I cannot say how long (but I'm pretty sure I
haven't experienced this for a very long time, otherwise I would have
reported it earlier, though possibly my usage wrt condition 2 has
changed, making this appear more frequently for me).

Is this a Gnus bug, or a Gmane bug, or am I overlooking some setting
that triggers this behavior?

Steve Berman