[Dovecot] Problem with 'doveadm mailbox status -t' reporting cumulative vsizes after upgrading from v2.0.16 to v2.1.7

[Jase Thew]

Hi,

I upgraded from Dovecot v2.0.16 to v2.1.7 over night and I noticed this
morning that one of my daily reports which lists summarised mailbox
sizes per user has started listing nonsense for vsizes.

The reporting script at its core calls :

doveadm -f flow mailbox status -A -t 'messages vsize' '*'

It appears that Dovecot 2.1.7 is not resetting the vsize after collating
the sum total of mailboxes sizes for each user, so that vsize just
constantly increases as it iterates over each user.

Eg:

# doveadm -f flow mailbox status -A -t 'messages vsize' '*'

accounts at example.com messages=1 vsize=759
adam at example.com messages=0 vsize=759
amy at example.com messages=24 vsize=51699697
andy at example.com messages=5446 vsize=3220940815
anna at example.com messages=50 vsize=3224035563
careers at example.com messages=1 vsize=3224036311
craig at example.com messages=2471 vsize=4421343199
creative at example.com messages=189 vsize=4426884182
david at example.com messages=8 vsize=4440729729
davidw at example.com messages=0 vsize=4440729729
enquiries at example.com messages=1 vsize=4440730491
gemma at example.com messages=4109 vsize=6349098844
gin at example.com messages=86 vsize=6392599904
holly at example.com messages=2000 vsize=7200342663
ian at example.com messages=0 vsize=7200342663
info at example.com messages=4 vsize=7200558689
jackie at example.com messages=2 vsize=7200721146
jade at example.com messages=137 vsize=7210548548
jake at example.com messages=16667 vsize=15260532446
katie at example.com messages=1 vsize=15260533375
mark at example.com messages=0 vsize=15260533375
mike.a at example.com messages=9 vsize=15261474205
mike.s at example.com messages=296 vsize=15314352543
mike at example.com messages=6357 vsize=20631446344
nick at example.com messages=1184 vsize=21038046728
social at example.com messages=65 vsize=21038935461
will at example.com messages=85 vsize=21057572390
[SNIP]

The same occurs with -u '*@example.com' in place of -A, and also for
'all' in place of 'messages vsize'.

Is this expected behaviour in 2.1.x compared to 2.0.x, or have I
stumbled upon a bug?

Regards,

Jase Thew.