cyrus expire omits one user's INBOX

[Gijs Hillenius]

The INBOX of one of the users on my Cyrus Imap server is piling up
messages that are marked for deletion, yet not expunged. These messages
do not show up in any mail client, so I'm assuming they're correctly
marked as deleted¹.

It seems this user's INBOX (it's mine, actually) is not included in the
daily cyr_expire run, whereas the inboxes of other users are.

Quote from syslog

cyr_expire  Repacking mailbox user.user1
cyr_expire  Repacking mailbox user.user2
cyr_expire  Repacking mailbox user.me.folder[1-4]
cyr_expire  Repacking mailbox user.user4
cyr_expire  Repacking mailbox user.user4.folder
cyr_expire  Repacking mailbox user.user5
etcetera

I would expect a "Repacking mailbox user.me" too :-)

The server is running Cyrus 2.4.17 from Debian stable (Jessie).

cyradm shows:

localhost> info user.me
{user.me}:
  duplicatedeliver: false
  lastpop:  
  lastupdate: 14-Jan-2016 12:08:44 +0100
  partition: default
  pop3newuidl: true
  sharedseen: false
  size: 177414
localhost> lam user.me
me lrswipcda

I've run reconstruct -fr user.me
I've run quota -f user.me

from cyrus conf:
delprune        cmd="/usr/sbin/cyrus expire -E 3" at=0401


the INBOX currently has a 161 messages, of which I'd expected all those
from before Jan 12 to be deleted. Yet there are 19 files dating from
January 11.

1) What is the best way to check the delete flag from these 160
messages?

mbexamine user.me | less

 Index Header Info:
  Generation Number: 285646
  Minor Version: 12
  Header Size: 128 bytes  Record Size: 96 bytes
  Number of Messages: 17  Mailbox Size: 1167022 bytes
  Last Append Date: (1452846705) Fri Jan 15 09:31:45 2016
  UIDValidity: 1219570297  Last UID: 132313
  Deleted: 0  Answered: 0  Flagged: 0
  Mailbox Options: POP3_NEW_UIDL
  Last POP3 Login: (0) Thu Jan  1 01:00:00 1970
  Highest Mod Sequence: 91074

and then shows the details for the 17 messages visible in the INBOX, and
then for those in all of the folders. How can I see the details for the
other messages, the ones I would expect to be removed from the file
system?