[Dovecot] Debian Wheezy-Backports - Dovecot (1:2.2.9-1~bpo70+1) missing xz compression support?

[T.B.]

Hallo Everyone,

since some days a new dovecot version is available in Debian 
"wheezy-backports": (1:2.2.9-1~bpo70+1) wheezy-backports

As described in http://wiki2.dovecot.org/Plugins/Zlib and 
http://www.dovecot.org/doc/NEWS-2.2 "xz"-compression is available since 
Dovecot version 2.2.9.

Today I tried to convert my mailboxes with the new xz compression.

Therfore I changed my config as follows:

/etc/dovecot/conf.d/10-mail.conf:
# Space separated list of plugins to load for all services. Plugins 
specific to IMAP, LDA, etc. are added to this list in their own .conf files.
mail_plugins = zlib acl fts fts_solr

/etc/dovecot/conf.d/90-plugin.conf:
# Enable these only if you want compression while saving:
   zlib_save_level = 9 # 1..9
   zlib_save = xz # gz or bz2 or xy


Now I tried to convert my mailboxes - but somehow, something goes wrong:

root at SERVER:/# dovecot --version
2.2.9
root at SERVER:/# dsync mirror mdbox:/srv/converted_vmail/
doveadm(root): Error: zlib_save: Support not compiled in for handler: xz
dsync(root): Error: zlib_save: Support not compiled in for handler: xz


Where is the failure?
Did the packet maintainer forget to activate xz?

I can't find anything xz related in the debian package changelog:
http://metadata.ftp-master.debian.org/changelogs//main/d/dovecot/dovecot_2.2.9-1~bpo70+1_changelog

Should I contact the Debian packet maintainer?
http://packages.qa.debian.org/d/dovecot.html

Best regards

T.B.