Line 2169: Table 3-6 - PUBREC Reason Codes:
add code value 150 (0x96) "Message rate too high" to the table.

Line 881: Table 2-4 Reason Codes
add PUBREC in the Packets column for Value 150 (0x96) "Message rate too high"

This code is different than return code 151 and needed for PUBACK, to inform the Sender that it has temporarily exceeded the throughput limit (vs. the cumulative (daily/monthly) quota for a customer, represented by value 151).

Example: Sender can wait for a period of time and then continue sending messages, instead of forcing it to disconnect and perform a resource intense reconnect.

This issue was originally reported in MQTT-417, which doesn't seem to be applied in WD14.