[Sieve] Unable to fileinto subfolders

[james]

Hello again list!

I am configuring a server running Dovecot 2.2.15 (Pigeonhole 0.4.6), and 
I am having an issue with Sieve scripts where I cannot sort messages 
into a subfolder of a mailbox. An email which is matched by the 
following script:

require "fileinto";
if header :contains "Subject" "[SORT ME]" { fileinto "INBOX.Sorted"; }

Yields the following error:

Jul 16 18:54:46 smtp dovecot: lmtp(ja...@lottspot.vpn): Error: 
DiJmNGZgqFWLFAEANWXNPw: sieve: msgid=<4973528.yvy4Yu8Tt4@arch_project>: 
failed to store into mailbox 'INBOX.Sorted': Character not allowed in 
mailbox name: '.'

As far as I can tell based on the Sieve usage page in the wiki 
(http://wiki2.dovecot.org/Pigeonhole/Sieve/Usage), this is *supposed* to 
work. I have included my namespace configuration below, but if anyone 
wants the whole doveconf -n, I will gladly provide it. Thanks in advance 
for any help!

namespace inbox {
  type = private
  separator = /
  prefix =
  inbox = yes
  mailbox Drafts {
    auto = subscribe
    special_use = \Drafts
  }
  mailbox Sent {
    auto = subscribe
    special_use = \Sent
  }
  mailbox Spam {
    auto = subscribe
    special_use = \Junk
  }
  mailbox Trash {
    auto = subscribe
    special_use = \Trash
  }
}
namespace {
  type = shared
  separator = /
  prefix = shared/%%d/%%n/
  location = 
maildir:/home/%%d/%%n/mail:INDEX=~/indexes/%%d/%%n:INDEXPVT=~/indexes/%%d/%%n
  subscriptions = no
  list = children
}