deleting instead of expiring mail

[Adrian Lanz <lanz@wsl.ch>]

Help, I am suddenly loosing old mails - they are deleted instead of
expired (for some 3 weeks now). I am on Gnus v5.13.

I am not aware of any changes in my configuration. Possibly, I may have
experimented with a nnvirtual group (nnvirtual "^nnfolder\\+mail.*$")

The log in the *Message* buffer seems a bit suspicious (just a snippet
for one of the groups with C-c C-M-x gnus-group-expire-all-groups) -
where comes the "Deleting articles..." from? Is this correct?

  Expiring articles in nnfolder+mail:noreply@ecoapwebsite.eu...
  Deleting articles...done
  Expiring articles in nnfolder+mail:noreply@ecoapwebsite.eu...done

My relevant entries since always are:

  (setq-default nnmail-expiry-wait-function
		(lambda (group)
		  (cond ((string= group "spam.mail") 5)
			((string= group "root@sampling") 5)
			(t 30)))
		gnus-total-expirable-newsgroups "nnfolder\\+mail:.*"
		gnus-mark-copied-or-moved-articles-as-expirable t
		nnmail-expiry-target 'nnmail-fancy-expiry-target
		nnmail-fancy-expiry-targets
		'(("xref" "spam\\.mail:[01-9]" "nnml+expired:spam.%Y")
		  (to-from "root@sampling" "nnml+expired:sampling-root-%Y")
		  (to-from "et\\.com" "nnml+expired:et-%Y")
		  (to-from "ws\\.com" "nnml+expired:ws-%Y")
		  (to-from ".*" "nnml+expired:other-%Y"))))


  (setq-default gnus-select-method '(nnnil "")
	        gnus-secondary-select-methods
	        `((nntp "news.gmane.org")
		  (nnfolder "mail"
                            [...]
			    (nnfolder-get-new-mail t)
			    (nnfolder-inhibit-expiry nil))

   		  (nnml "expired"
                        [...]
		        (nnml-get-new-mail nil)
		        (nnml-inhibit-expiry t))


And, expiry of spam and sampling-root continuous to work as expected,
but the (important!) mails in the other groups in nnfolder+mail:* get
lost!