JAVA_OPTS not honoured

If I set the JAVA_OPTS environment variable to, e.g.:

$ echo $JAVA_OPTS
-Xms256m -Xmx2048m -XX:PermSize=128m -XX:MaxPermSize=1200m

and then start a Play 2.2 application (the default Java one generated using "play new app"), the options are not honoured. jconsole shows:

-Xms1024m
-Xmx1024m
-XX:MaxPermSize=256m

This is contrary to the behaviour documented by "bin/app -help":

$ bin/app -help
Usage:  [options]

  -h | -help         print this message
  -v | -verbose      this runner is chattier
  -d | -debug        set sbt log level to debug
  -mem    <integer>  set memory options (default: , which is -Xms1024m -Xmx1024m -XX:MaxPermSize=256m -XX:ReservedCodeCacheSize=128m)
  -jvm-debug <port>  Turn on JVM debugging, open at the given port.

  # java version (default: java from PATH, currently java version "1.6.0_65")
  -java-home <path>         alternate JAVA_HOME

  # jvm options and output control
  JAVA_OPTS          environment variable, if unset uses ""
  -Dkey=val          pass -Dkey=val directly to the java runtime
  -J-X               pass option -X directly to the java runtime
                     (-J is stripped)

In the case of duplicated or conflicting options, the order above
shows precedence: JAVA_OPTS lowest, command line options highest.