[Dovecot] quota not being calculated

[Cor Bosman]

It looks like my quota isnt being calculated properly after I started setting quota to a specific folder. The quota in that folder is always starting out at 0, and only new email is being added to the quota. If I remove the maildirsize file, and recalculate, it still starts at 0. Once email arrives in the folder, it gets added to maildirsize. This is with maildirquota, in perhaps a bit of an exotic config. The idea is to set a specific quota to Spam folder, using the trash plugin to keep it at a certain size. 

. getquotaroot "Spam"
* QUOTAROOT "Spam" "User quota" "Spam quota"
* QUOTA "User quota" (STORAGE 40848 1228800)
* QUOTA "Spam quota" (STORAGE 0 20000)
. OK Getquotaroot completed.

Once 1 email gets added:

.Spam# cat maildirsize 
20480000S
0 0
2017 1


namespace {
  hidden = no
  ignore_on_failure = no
  inbox = yes
  list = yes
  location = maildir:%h:INDEX=/var/spool/mail/dovecot-control/indexes/%1u/%2u/%u:CONTROL=/var/spool/mail/dovecot-control/%1u/%2u/%u/INBOX
  prefix = 
  separator = /
  subscriptions = yes
  type = private
}
namespace spam {
  hidden = yes
  ignore_on_failure = no
  inbox = no
  list = yes
  location = maildir:%h/.Spam:INDEX=/var/spool/mail/dovecot-control/indexes/%1u/%2u/%u/.Spam:CONTROL=/var/spool/mail/dovecot-control/%1u/%2u/%u/.Spam
  prefix = Spam/
  separator = /
  subscriptions = no
  type = private
}

plugin {
  quota = fs:User quota
  quota2 = maildir:Spam quota:ns=Spam/
  quota2_rule = *:storage=20000K
  sieve = /var/spool/mail/dovecot-control/sieve/%1u/%2u/%u/dovecot.sieve
  sieve_before = /etc/sieve/before
  sieve_dir = /var/spool/mail/dovecot-control/sieve/%1u/%2u/%u/scripts
  trash = /etc/dovecot/conf.d/dovecot-trash.conf.ext
}

(full config:  http://pastebin.com/Mui4X7Zh)