expiry-target group parameter does not have any effect

[Alexander Baier]

Hello!

I just turned on auto-expire in one of my groups with the group
parameters configured as follows:

;;; Editing the group parameters for `nnmaildir+mailbox:INBOX.daily'.
((auto-expire . t)
 (expiry-wait . 14)
 (expiry-target . "nnmaildir+mailbox:Trash"))

I expect read articles older than 14 days to be moved to the group
"nnmaildir+mailbox:Trash".  But this does not happen.  Said articles are
correctly deleted in their original group, but nothing appears in the
Trash group.

Did I mess up my configuration?  Is there a way to "track" the expiry
process, so I can find out, what is going wrong?

TIA,
-- 
Alexander Baier