Minor We need to have consistency in the usage of malformed control packets and protocol errors .
In PUBLISH 3.3.5 we say
1) A Topic Alias value of zero or greater than the Maximum Alias is a protocol error, the receiver MUST send a DISCONNECT Packet with a 0x82 (Protocol error) Return code and then close the Network Connection.
The client has been authenticated so there is no reason to hide the detection of a malformed packet or protocol error hence we should mandate the sending of the disconnect packet.
In section 4.13 Handling errors.
Remove the "MUST close the Network Connection" in the case of protocol errors, otherwise the receiver is required to detect every possible protocol error.