[Dovecot] Keyword limit?

[Michael M Slusarz]

Running into a weird issue in a mailbox that has 26+ keywords.

In one session, I do this:

S: 2 SELECT "INBOX" (QRESYNC (1255685337 78608 [...uids...]))
S: [...]
S: * OK [HIGHESTMODSEQ 78608] Highest
S: * OK [UIDVALIDITY 1255685337] UIDs valid
S: 2 OK [READ-WRITE] Select completed.
C: 3 UID STORE 48386 (UNCHANGEDSINCE 78608) +FLAGS AAAAAAAA
S: * 8 FETCH (UID 48386 MODSEQ (78609) FLAGS (\Seen AAAAAAAA))
S: 3 OK Store completed.
C: 4 LOGOUT
S: * OK [CLOSED] Previous mailbox closed.
S: * BYE LOGOUT received
S: 4 OK Completed

The next time I access that mailbox, I see this:

C: 2 SELECT "INBOX" (QRESYNC (1255685337 78609 [...uids...]))
S: [...]
S: * OK [UIDVALIDITY 1255685337] UIDs valid
S: * OK [HIGHESTMODSEQ 78609] Highest
S: * 8 FETCH (MODSEQ (78610) UID 48386 FLAGS (\Seen))
S: 2 OK [READ-WRITE] Select completed.

MODSEQ 78610 is entirely server-initiated.

It *appears* that the mailbox doesn't handle more than 26 keywords.   
My dovecot-keywords looks like:

0 $Forwarded
[Entries 1-24]
25 Test

"Test" is a keyword I created immediately before "AAAAAAAA".  If I  
remove Test and then add "AAAAAAAA", the keyword sticks.

Is this a built-in limit?  Can't find anything in the config/wiki docs  
(Dovecot 2.1.16).  Or are my dovecot index/cache files hosed in some  
way?

michael