OF should not silently close a connection, when receiving a message without 'to' attribute
If Openfire receives a message with no 'to' attribute, it closes the connection (even without stream error, but which would be wrong behavior, too).
The correct behavior is:
If the server receives a message stanza with no 'to' attribute, it MUST treat the message as if the 'to' address were the bare JID <localpart@domainpart> of the sending entity.
In the error logs you can read this: