Indeed, accountsservice sends a reply even when the client talking to it doesn't want one. The dbus daemon doesn't remember messages that have NO_REPLY_EXPECTED set, so the replies from accountsservice look like unsolicited messages to it and it denies them.
Gnome bug #755421 argues that this should be fixed in gdbus, and I agree. gdbus automatically sets NO_REPLY_EXPECTED when no callback is given, so it makes sense that it also handles the server side by discarding replies for such messages. I've attached a patch upstream.
Indeed, accountsservice sends a reply even when the client talking to it doesn't want one. The dbus daemon doesn't remember messages that have NO_REPLY_EXPECTED set, so the replies from accountsservice look like unsolicited messages to it and it denies them.
Gnome bug #755421 argues that this should be fixed in gdbus, and I agree. gdbus automatically sets NO_REPLY_EXPECTED when no callback is given, so it makes sense that it also handles the server side by discarding replies for such messages. I've attached a patch upstream.