message moved by a filter is not shown up in Messaging Menu due to "not NEW"

A message moved by a filter is not shown up in MessagingMenu.

the log says:
Rejecting message: Message is not new

It is reproducible only with POP account as far as I tested.

thunderbird: 17.0.2+build1-0ubuntu0.12.04.1
messagingmenu: 1.3.1

How to reproduce:
 1. set up POP account (I used Gmail account with POP connection)
 2. create a folder "filtered" under POP account
 3. create a filter to move massages with the title "foo" into the folder "filtered"
 4. send a message to yourself with the title "foo", then receive it

Expected result:
 total new message count in icon badge will be incremented,
 and it will be shown up with the folder name "filtered" under Messaging Menu.

Actual result:
 total new message count in icon badge will not be incremented,
 Messaging Menu does not contain any entry with the folder name "filtered".

I didn't know how to get output from LOG(), so I changed LOG() to ERROR(), then I got messages in error console.
====
messagingmenu: Item mailbox-message://<MY_ACCOUNT>%<email address hidden>/filtered#3 added to mailbox:///home/nmurata/.thunderbird/8ni150jy.notify-test/Mail/pop.googlemail.com/filtered

messagingmenu: Applying filter for message mailbox-message://<MY_ACCOUNT>%<email address hidden>/filtered#3 in mailbox:///home/nmurata/.thunderbird/8ni150jy.notify-test/Mail/pop.googlemail.com/filtered

messagingmenu: Rejecting message: Message is not new
====