The template policy located at $DERBY_HOME/demo/templates/server.policy (release distributions) and $trunk/java/drda/org/apache/derby/drda/template.policy (source tree) contains a comment relating to JMX permissions which says:
// JMX management of Derby is NOT enabled by default; see also
This was no longer true after
DERBY-3429 was fixed, which includes the 10.4.1.3 release. JMX monitoring and management is enabled by default given that the JVM includes the required APIs, and that the security policy allows JMX features to come up. The comment should have been removed, but this has not happened. The same applies to the default server policy, server.policy, which also should be corrected (this policy's comments are however not exposed to users in the same way as the template).
Note that no code or actual permissions need to change as a result of this; it is merely an outdated comment that needs to be removed in order not to give users a false impression.