Character not allowed in mailbox name

[Lothar Schilling via dovecot]

Hi everybody,

after an update this morning to dovecot 2.3.7 we cannot connect to our
shared mailboxes anymore. The error message as issued in Thunderbird:

"Character not allowed in mailbox name '.'"

I didn't change anything about the configuration. Output of dovecot -n:

[...]
namespace {
  list = children
  location = maildir:%%h:INDEX=%h/shared/%%u
  prefix = Shared/%%u/
  separator = /
  subscriptions = yes
  type = shared
}
[...]

Any help would be appreciated, thank you very much.

Lothar Schilling