Maildir to mdbox conersion size issue

Hello,

I have issue with dovecot 2.2.13

I want to change all Maildirs to mdbox format and I do it per partes, so I change mail_location for user (in sql), than I use doveadm sync -u user path_to_maildir and everything works mostly fine.

But now I found that when I migrate quite huge Maildir (about 24G of mails) to mdbox, after sync the final mdbox is twice as big as source Maildir (48GB). I tried to find duplicities, but didn't find any.

Is there any reason why mdbox consume so much data? Or I do something wrong?

Does somebody have same experience?

Thanks

Petr