MQTT disconnect when AT+QMTPUB with retain=1

IoT Modules
1

PUB with retain=0 will maintain the connection:

AT+QMTPUB=3,99,1,0,"topic"
> {"msg":"Hello"} ^Z
OK
+QMTPUB: 3,99,0

But PUB with retain=1 will cause the connection to drop:

AT+QMTPUB=3,99,1,1,"topic"
> {"msg":"Hello"} ^Z
OK
+QMTSTAT: 3,1

Is this expected?

2

It is possible that the MQTT server does not support this configuration and the server is disconnected.