[Dovecot] dsync / separator / namespace config-problem

Guess I don't quite get namespaces, but we have the following namespace configured:

$ doveconf namespace
namespace {
	hidden = no
	inbox = yes
	list = yes
	location = 
	prefix = INBOX.
	separator = 
	subscriptions = yes
	type = private
}

But when I try running dsync it complains:

$ sudo -u atmail dsync   -u janfrode@tanso.net mirror mdbox:/tmp/janfrodeboks
dsync(atmail): Error: user janfrode@tanso.net: Initialization failed: namespace configuration error: list=yes requires prefix=INBOX. to end with separator dsync(atmail): Fatal: User init failed

I can fix this by adding "separator = ." to the namespace and dsync is happy, but is changing this now safe, or will this affect existing clients?

-jf