[Dovecot] search and UTF-8 normalization forms (NFD)

Hello,

on a system with dovecot 2.2 I've got a mailbox containing multiple mails from a person called Krüger, but From: header encoded differently. Some are encoded in UTF-8 normalization form decomposed (as used by Mac OSX), that is u and umlaut accent as sperate combined codepoints instead of one ü:

From: =?utf-8?Q?replaced_Kru=CC=88ger?= krueger@some.domain

Searching within roundcube webmail for "krüger" as sender missis this mails.

Roundcube sends (dovecot rawlog): A0003 UID THREAD REFS UTF-8 ALL HEADER FROM {7+}krüger

Is this supposed to work? Haven't done any more debugging (other search variants) or read RFCs. As a user I would expect Unicode equivalence rules be applied (see http://en.wikipedia.org/wiki/Unicode_equivalence)

Regards, Lutz