I am not sure this is a bug. I have opened a thread in the jboss community. But so far I have not got a definitive answer. I can reproduce this everytime.
This same code works fine in eap 6.0.

Please see the issue description in the following thread:
https://community.jboss.org/thread/237883

I would like to provide more details if somebody will work on this issue.

Server log and trace level log (jca trace) are attached on that thread.

Thanks.