What made ticked/unread articles becomes OLD ?!

[Danny Siu <dsiu@Adobe.COM>]

In my mail folder named "Active" (using nnfolder backend), after I do 'g' in
the summary buffer, all of the sudden all unread (no mark) and ticked ("!")
articles becomes old ("O") and hence hidden in the summary buffer!  C-u ret
in that reveals that articles that I ticked and articles with no marks has
been magically marked old.  This doesn't happen every time I get mail,
though, but it happens like once a month.  Does anyone know can this happen?
Is this a bug in Gnus?  I am using 5.4.42.

Here are variables related to the expire:

(setq nnmail-expiry-wait-function
      (function (lambda (group)
		  (cond ((string-match "Active" group) 21)
			((string-match "Other-Friends" group) 14)
			((string-match "Fvwm" group) 1)
			((string-match "MD" group) 1)
			(t nnmail-expiry-wait)))))

(setq gnus-auto-expirable-newsgroups "Active\\|Other-Friends\\|Fvwm\\|MD")

I am using all the default group parameters for "Active". (ie: total-expire
and expiry-wait are not set to any values)

Thanks!
-- 
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|  Danny Dick-Fung Siu                http://www-leland.stanford.edu/~dsiu |
|  Reference System Group             http://www.csua.berkeley.edu/~dsiu   |
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