Tomcat fails to stop with "Port already in use" when enabling jmx remote monitoring

Issue

We are setting the following java options to JAVA_OPTS in order to enable jmx remote monitoring:

JAVA_OPTS="$JAVA_OPTS -Xms1024m -Xmx2048m"
JAVA_OPTS="$JAVA_OPTS -XX:PermSize=256m -XX:MaxPermSize=256m"
JAVA_OPTS="$JAVA_OPTS -verbose:gc -Xloggc:gc.log -XX:+PrintGCDetails -XX:+PrintGCTimeStamps"
JAVA_OPTS="$JAVA_OPTS -XX:+HeapDumpOnOutOfMemoryError"
JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote"
JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote=true"
JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote.ssl=false"
JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote.authenticate=false"
JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote.port=12345" 

Then the following error is shown when executing catalina.sh stop or service tomcat6 stop command:

Error: Exception thrown by the agent : java.rmi.server.ExportException: Port already in use: 12345; nested exception is: 
    java.net.BindException: Address already in use

Then we have to stop Tomcat java process with kill command like: $kill <TOMCAT_JAVA_PID>