Translucency is not working on Linux using Metacity

J2SE Version (please include all output from java -version flag):
java version "1.6.0_10"
Java(TM) SE Runtime Environment (build 1.6.0_10-b33)
Java HotSpot(TM) Client VM (build 11.0-b15, mixed mode, sharing)

Does this problem occur on J2SE 5.0.x or 6.0? Yes / No (pick one)
Yes

Operating System Configuration Information (be specific):
Linux Ubuntu 7.10
Window Manager: Metacity
xdpyinfo:
name of display: :0.0
version number: 11.0
vendor string: The X.Org Foundation
vendor release number: 10300000
X.Org version: 1.3.0
maximum request size: 16777212 bytes
motion buffer size: 256
bitmap unit, bit order, padding: 32, LSBFirst, 32
image byte order: LSBFirst
number of supported pixmap formats: 7
supported pixmap formats:
    depth 1, bits_per_pixel 1, scanline_pad 32
    depth 4, bits_per_pixel 8, scanline_pad 32
    depth 8, bits_per_pixel 8, scanline_pad 32
    depth 15, bits_per_pixel 16, scanline_pad 32
    depth 16, bits_per_pixel 16, scanline_pad 32
    depth 24, bits_per_pixel 32, scanline_pad 32
    depth 32, bits_per_pixel 32, scanline_pad 32
keycode range: minimum 8, maximum 255
focus: window 0x2801083, revert to Parent
number of extensions: 29
    BIG-REQUESTS
    Composite
    DAMAGE
    DPMS
    Extended-Visual-Information
    MIT-SCREEN-SAVER
    MIT-SHM
    MIT-SUNDRY-NONSTANDARD
    RANDR
    RECORD
    RENDER
    SECURITY
    SHAPE
    SYNC
    TOG-CUP
    X-Resource
    XAccessControlExtension
    XC-APPGROUP
    XC-MISC
    XFIXES
    XFree86-Bigfont
    XFree86-DGA
    XFree86-Misc
    XFree86-VidModeExtension
    XINERAMA
    XInputExtension
    XKEYBOARD
    XTEST
    XVideo
default screen number: 0
number of screens: 1

screen #0:
  dimensions: 800x600 pixels (323x242 millimeters)
  resolution: 63x63 dots per inch
  depths (7): 16, 1, 4, 8, 15, 24, 32
  root window id: 0x3b
  depth of root window: 16 planes
  number of colormaps: minimum 1, maximum 1
  default colormap: 0x20
  default number of colormap cells: 64
  preallocated pixels: black 0, white 65535
  options: backing-store NO, save-unders NO
  largest cursor: 800x600
  current input event mask: 0xfa0033
    KeyPressMask KeyReleaseMask EnterWindowMask
    LeaveWindowMask StructureNotifyMask SubstructureNotifyMask
    SubstructureRedirectMask FocusChangeMask PropertyChangeMask
    ColormapChangeMask
  number of visuals: 2
  default visual id: 0x21
  visual:
    visual id: 0x21
    class: TrueColor
    depth: 16 planes
    available colormap entries: 64 per subfield
    red, green, blue masks: 0xf800, 0x7e0, 0x1f
    significant bits in color specification: 6 bits
  visual:
    visual id: 0x39
    class: TrueColor
    depth: 32 planes
    available colormap entries: 256 per subfield
    red, green, blue masks: 0xff0000, 0xff00, 0xff
    significant bits in color specification: 8 bits

Bug Description:

Translucency is not working on Linux using Metacity
According to the documentation Translucency on Linux using Metacity should work: 'X11: if running a composite (or compositing window-) manager like Compiz'.

Run the code below:

Expected:
* All 4 buttons to be enabled.
* The 'Output Graphics Configurations' button should output the Graphics Configurations
* The 'Test PERPIXEL_TRANSLUCENT' button should show a frame with the left third completely transparent (the cursor will control whatever is under it),
the middle third very transparent (the crosshair cursor should be shown when over this third),
the right third semi translucent (half way between red and the underlying color)
* The 'Test PERPIXEL_TRANSPARENT' button should show a circle shaped frame
* The 'Test TRANSLUCENT' button should show a a semi translucent frame

Actual:
* The first 3 buttons are enabled and the 'Test TRANSLUCENT' button is not
* The 'Output Graphics Configurations' button outputs:
X11GraphicsConfig[dev=X11GraphicsDevice[screen=0],vis=0x21] is Translucency Capable: false
X11GraphicsConfig[dev=X11GraphicsDevice[screen=0],vis=0x39] is Translucency Capable: true
* The 'Test PERPIXEL_TRANSLUCENT' button shows a Frame with the left two thirds completely black (with the crosshair cursor),
the right third is half way between red and black [this is a very big problem - we can't have users seeing that]
* The 'Test PERPIXEL_TRANSPARENT' button should show a circle shaped frame (this works as expected)
* isTranslucencySupported(TRANSLUCENT) is returning false so we don't even know the results here