Please see pematous's comment:
https://issues.jboss.org/browse/ENTMQBR-474?focusedCommentId=13390527&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13390527

Note: On ER18 this is only happens on durable messages after broker restart.

Reproduction scenario
1. start the broker
2. create durable queue
3. send a durable message towards the durable queue
4. stop the broker
5. start the broker
6. receive message
7. observe that the priority has changed from 4 to 0

This happens when the priority on the message is explicitly set as well, so there is probably an issue in the read/write process on the persistence store.

Please feel free to reopen as new bug if you believe it's completely different problem.
Also, I'm correcting the title of this Jira which was originally wrong.

[2017-04-06 01:51:12,233] [PASS] dtestlib.Test :: [root@<hostname>]$  java  -jar /var/dtests/node_data/clients/amqx.jar  queue --host <hostname>:1099 --action add --name "test_node_durable_msg_queue" --durable # ecode:0 (exp. 0), dur.:0.87 
[2017-04-06 01:51:14,370] [PASS] dtestlib.Test :: [root@<hostname>]$  /var/dtests/node_data/clients/aac5_sender.py  --broker-url "admin:admin@<hostname>:5672/test_node_durable_msg_queue" --log-msgs dict --count 1 --msg-durable True # ecode:0 (exp. 0), dur.:0.44 
[2017-04-06 01:51:16,827] [PASS] dtestlib.Test :: [root@<hostname>]$ runuser -s ${SHELL} jamq -c 'cd ~;/opt/jboss-amq-7-i0/bin/artemis-service stop' # ecode:0 (exp. True), dur.:1.15 
[2017-04-06 01:51:39,151] [PASS] dtestlib.Test :: [root@<hostname>]$ runuser -s ${SHELL} jamq -c 'cd ~;/opt/jboss-amq-7-i0/bin/artemis-service start' # ecode:0 (exp. True), dur.:1.21 
[2017-04-06 01:52:03,354] [PASS] dtestlib.Test :: [root@<hostname>]$  /var/dtests/node_data/clients/aac5_receiver.py  --timeout 2 --broker-url "admin:admin@<hostname>:5672/test_node_durable_msg_queue" --log-msgs dict --count 1 # ecode:0 (exp. 0), dur.:0.33 
[2017-04-06 01:52:03,355] [PASS] dtestlib.Test :: Check message count # result:1 (exp. 1), dur.:-1.00 
[2017-04-06 01:52:03,372] [FAIL] dtestlib.Test :: Messages compare # result:False (exp. True), dur.:-1.00 err_cnt:1
[2017-04-06 01:52:03,372] [FAIL] dtestlib.MessagingProcessor :: BEGIN comparison details vvvvvvvvv
  a_data = [{'creation_time': 0.0, 'first_acquirer': False, 'correlation_id': None, 'ttl': 0, 'reply_to_group_id': None, 'subject': None, 'content': 'None', 'delivery_count': 0, 'user_id': '', 'durable': True, 'id': None, 'priority': 4, 'content_encoding': 'None', 'annotations': None, 'body': 'None', 'content_type': 'text/plain', 'address': None, 'properties': {}, 'instructions': None, 'inferred': False, 'expiration': 0, 'reply_to': None, 'group_id': None, 'group_sequence': 0}]
  b_data = [{'creation_time': 0.0, 'first_acquirer': False, 'correlation_id': None, 'ttl': 0, 'reply_to_group_id': None, 'subject': None, 'content': 'None', 'delivery_count': 0, 'user_id': '', 'durable': True, 'id': None, 'priority': 0, 'content_encoding': 'None', 'annotations': None, 'body': 'None', 'content_type': 'text/plain', 'address': None, 'properties': {}, 'instructions': None, 'inferred': False, 'expiration': 0, 'reply_to': None, 'group_id': None, 'group_sequence': 0}]
  ab_diff = [{'priority': 4}]
  ba_diff = [{'priority': 0}]
  inflt = None
  exflt = ['JMSXDeliveryCount']