dovecot - Jan 2014 - error when running fts optimize

Since yesterday, when I run "fts optimize", I get an error.

Command:
doveadm -v fts optimize -u formulaire

Error:
Jan 10 18:05:20 mba dovecot: indexer-worker(formulaire): Error: lucene
index /mba_data/emails/formulaire/lucene-indexes: IndexWriter::optimize()
failed (#9): bit out of range

Does anyone have any idea what causes this and how to fix it?

Thanks,

Joe Beaubien