Bug entering summary from group buffer with dormant articles

[Chris Brierley <brierley@pobox.com>]

Gnus v5.8.5
GNU Emacs 20.6.1 (i386-*-windows98.1998)

I have an nnimap group where I've marked a number of articles as
dormant (?).  Upon re-entering that group later from the *Group*
buffer, Gnus barfs with the following backtrace (note
"CI-RESPONSE" is part of the subject of the messages marked as
dormant).

If I enter the group with C-u RET, I can successfully enter the
group, but the articles that I most recently marked as dormant are
now marked as ticked (!).  If I mark them all, again, as dormant
and exit, the problem seems to disappear.  I can re-enter the
group without the below error, and the messages stay marked dormant.

,-----
| Signaling: (wrong-type-argument number-or-marker-p CI-RESPONSE)
|   gnus-sorted-complement((759 762 2052 2726 2909 2916 2918 2934 2938 2960 3055 3073 3096 3097 3103 3166 3207 3208 3209 3210 3211 3212 3213 3214 3215 3216 CI-RESPONSE) (759 762 2052 2726 2909 2916 2918 2934 2938 2960 3055 3073 3096 3097 3103 3166 3207 3208 3209 3210 3211 3212 3212 3213 3213 3214 3214 3215 3215 3216 3216))
|   gnus-select-newsgroup("nnimap+ct:mail/ci" nil nil)
|   gnus-summary-read-group-1("nnimap+ct:mail/ci" nil t nil nil nil)
|   gnus-summary-read-group("nnimap+ct:mail/ci" nil t nil nil nil nil)
|   gnus-group-read-group(nil t)
|   gnus-group-select-group(nil)
|   gnus-topic-select-group(nil)
|   call-interactively(gnus-topic-select-group)
`-----