How are you doing the rendering into the JFrame? AWTGLRenderer, software renderer or an image taken from the FrameBuffer?
I'm just creating the frame buffer instance after the jframe is created
buffer = new FrameBuffer(app.getSettings().getWidth(), app.getSettings().getHeight()-125, FrameBuffer.SAMPLINGMODE_NORMAL);
this is how I'm getting the 2D graphics to display in the buffer, or whatever
graphics = (Graphics2D) getBufferStrategy().getDrawGraphics();
and in the update loop, I'm just cycling this bit of code to render the scene
// Clear the previous frame
graphics.clearRect(0, 0, getWidth(), getHeight());
buffer.clear(Color.BLACK); // app.getSettings().getBackgroundColor());
app.getCurrentState().display3D(buffer); // This is the jPCT world..
buffer.update();
buffer.display(graphics); // 2D graphics
app.getCurrentState().display2D(graphics);
Sorry for the lack of technicality in details.. I'm still learning