MQTT Message ordering in MQTT v3.1.1

[bryantwang-cc]

If server sends messages with QoS 1 in the order of 1,2,3,4, and the client corresponds the PUBACKs in the order of 1,3,2,4, is it correct accroding to the description in MQTT_v3.1.1 section 4.6(MQTT-4.6.0-2) ？

It MUST send PUBACK packets in the order in which the corresponding PUBLISH packets were received (QoS 1 messages) [MQTT-4.6.0-2]

Here is another question：
The mosquitto just ignores the packet when it receives a PUBACK packet but not corresponding the PUBLISH packets in the inflight window, is it reasonable? Or mosquitto should drop the connection?