[Dovecot] pigeonhole and utf-8 error

Hi, now, I'm working with the last version of dovecot and pigeonhole sieve, and when apply a sieve filter on a new message, and it try to move this mail to a folder with special character like accent give me the error 'mailbox name not utf-8: ...'

Aug 17 09:22:40 imap1 dovecot: lmtp(19629,miel): Error: kea6K484akytTAAAJBW4rA: sieve: msgid= 1099311971.505.1282029699154.JavaMail.open-xchange@o.uib.es: failed to store into mailbox 'atenció': >mailbox name not utf-8: atenció

dovecot it's working without problem on this folder. I suppose it's a misconfiguration, but I don't find where...

Xavier