ToolStripMenuButton icon bug?

[nitroamos]

It seems that ToolStripMenuButton does not show my icon because it seems that attribute is used to display the submenu icon instead. Here's a test case. I've used the same image in two places to demonstrate that the path to the image is correct.

isc.Menu.create({
    ID: "docMenu",
    data: [
       {title: "User's Manual",
        // this usage correctly appears; proves the image exists:
        icon: "pieces/16/cubes_green.png"}
    ]
});

isc.ToolStripMenuButton.create({
    ID: "docMenuButton",
    title: "Documentation",
    // this icon is not appearing:
    icon: "pieces/16/cubes_green.png",
    menu: docMenu
});

isc.ToolStrip.create({
    members: [docMenuButton]
});

If I use

docMenuButton.setIcon("pieces/16/cubes_green.png");

then the submenu icon is replaced with cubes_green.png, which is not behavior I would have expected.

i.e. it doesn't appear to be possible to have both my icon and the submenu icon appear at the same time. The Reference Overview page for ToolStripMenuButton says that it is possible to display an "icon with text". Is this is a software bug or a documentation bug?

I'm using SmartClient 9.0 evaluation version on Safari 6.1.1.