Calling Java from Octave with double arguments loses precision - octave

Question

I'm running into a strange issue calling a Java library from Octave. I'm using the JSON library from http://www.json.org/java/. Here's an example Java class:
import org.json.JSONObject;
public class Test {
public static void main(String[] args) throws Exception {
JSONObject obj = new JSONObject();
obj.put("primitive", 3.1415926);
obj.put("wrapped", new java.lang.Double(3.1415926));
System.out.println(obj.toString());
}
}
and the corresponding code in Octave (I'm using 3.8.1):
function test()
javaaddpath('json.jar')
obj = javaObject('org.json.JSONObject');
obj.put('primitive', 3.1415926);
obj.put('wrapped', javaObject('java.lang.Double', 3.1415926));
disp(obj.toString());
end
When I compile and run the Java code, I of course get
{"wrapped":3.1415926,"primitive":3.1415926}
With Octave, on my OS X laptop, I get the same thing.
$ octave --eval test
warning: function ./test.m shadows a core library function
GNU Octave, version 3.8.1
Copyright (C) 2014 John W. Eaton and others.
This is free software; see the source code for copying conditions.
There is ABSOLUTELY NO WARRANTY; not even for MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. For details, type 'warranty'.
Octave was configured for "x86_64-apple-darwin14.0.0".
Additional information about Octave is available at http://www.octave.org.
Please contribute if you find this software useful.
For more information, visit http://www.octave.org/get-involved.html
Read http://www.octave.org/bugs.html to learn how to submit bug reports.
For information about changes from previous versions, type 'news'.
{"primitive":3.1415926,"wrapped":3.1415926}
But on my Ubuntu 12.04 VM, with Octave installed from ppa:octave/stable, I get:
$ octave --eval test
warning: function ./test.m shadows a core library function
GNU Octave, version 3.8.1
Copyright (C) 2014 John W. Eaton and others.
This is free software; see the source code for copying conditions.
There is ABSOLUTELY NO WARRANTY; not even for MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. For details, type 'warranty'.
Octave was configured for "i686-pc-linux-gnu".
Additional information about Octave is available at http://www.octave.org.
Please contribute if you find this software useful.
For more information, visit http://www.octave.org/get-involved.html
Read http://www.octave.org/bugs.html to learn how to submit bug reports.
For information about changes from previous versions, type 'news'.
{"wrapped":3,"primitive":3.1415926}
Somehow the java.lang.Double object turns into an integer, or at least the fractional part gets stripped off. What is going on here?