Unnecessary nntp reading?

[John Griffith <griffith@sfs.nphil.uni-tuebingen.de>]

I have all my mail (nnml) groups on levels 1 and 2 and all nntp groups
on 3 and 4.

I'm trying to figure out what several variables do and how they
interact with each other.  Namely the variables:
  - gnus-activate-level
  - gnus-read-active-file
  - gnus-check-new-newsgroups

A) If I set gnus-activate-level to 1 and gnus-check-new-newsgroups to
   nil I would suspect that the nntp server should not be read at all,
   but it is - even if gnus-read-active-file is nil as well. However,
   as I would expect, the nntp groups are not updated.  What is Gnus
   looking for?  It's not looking for newgroups and it's not looking
   for active information on my nntp groups.

B) If I set gnus-activate-level to 1 and gnus-check-new-newsgroups to
   nil and gnus-read-active-file to `some' then I would suspect that
   (regardless of A above) the nntp groups' active information would
   not be read - but they are.

The documentation for gnus-read-active-file says "If this variable is
`some', Gnus will try to only read the relevant parts of the active
file from the server."  I would think that the definition of a
"relevant part" should take into consideration that fact that if
gnus-activate-level is lower than all nntp groups (and no prefix
argument was given) then there are _no_ relevant parts.

Furthermore, what I would like (and expect) is that setting
gnus-activate-level to 3 and gnus-read-active-file to `some' would
allow me to put some "subscribed" nntp groups on level 4 but not have
their active information updated (and therefor not spend lots of time)
unless I use an explicit prefix argument to "M-x gnus" or "g" from the
group buffer, etc.

If these things are not bugs, then I think the documentation of these
variables should explain and motivate this behavior.