IMAP flags and dovecot-keywords not working as expected

[Mark Foley]

I've converted most of our users from Outlook to Thunderbird.  One important feature of
Thunderbird is that it pays attention to the IMAP non-standard message flags via the 'tags'
feature (see http://wiki2.dovecot.org/MailboxFormat/Maildir).  This is important because 2
users make extensive use of Outlook categories (Tags, in Thunderbird).  I found that when I set
a message to the 1st Tbird tag 0 (Important), the corresponding IMAP file got an 'a' suffix. 
Likewise, if I manually added an 'a' suffix to an IMAP file the corresponding tag was set
displayed in Thunderbird.  This made it easy for me to exports Outlook Categories and set IMAP
messages flags accordingly.  This worked perfectly on the user I was experimenting with (me). 

Recently, I converted one of these Outlook 'categories' users to Thunderbird.  I added the
appropriate flag letters to their IMAP messages, changed their tag names in Thunderbird, and
created the following dovecot-keywords file as:

0 Board_and_Committee
1 Completed
2 Health_Care_meetings
3 Notifications
4 OSHP-DAS
5 personal_or_To_Do
6 Retirement_exits
7 $label5
8 Junk
9 $Forwarded
10 $MDNSent
11 $label2

However, none of the tags show up correctly in Thunderbird.  If I manually set a message to
have a tag of 0, the corresponding IMAP file gets a flag of 'm', not 'a' and the following is
added to the dovecot-keywords files:

12 $label1

How can I fix this? Where is "$label1" text defined? Why did Thunderbird not snag the text for
'0' from the dovecot-keywords file and give the IMAP file a tag of 'a'?

My current theory is that the "Default" Thunderbird Tags corresponding to IMAP flags are not
changeable and if new tags are create in Tbird, they get new flag letters.  That would, of
course, mean that if a user changes Thunderbird tag name, they would lose all tag settings on
existing message.  That doesn't seem right and I hope my theory is wrong. 

Any insight would be appreciated.

--Mark