Transparency and Wireframe using Ardor3D

The following image illustrates transparency working correctly. The sphere has alpha set to 0.3 and we can see the bbox lines through the sphere:



However, if I rotate the model round slightly I can no longer see the bbox lines:



I get a similar result when I render one sphere entirely using wireframe; in this image we can see the wireframe sphere inside the transparent spehere:



and again, if I rotate the object round slightly transparency fails:



I use transparency as described in the RenderQueueExample and the following code used for preventing texture bleeding on the wireframe objects using the MeshData.setIndexMode(IndexMode.Lines):

        // turn off textures to prevent bleeding of texture coordinates from other shapes
        this.getSceneHints().setTextureCombineMode(TextureCombineMode.Off);
        this.getSceneHints().setLightCombineMode(LightCombineMode.Off);

Is there a known bug when using wireframe and transparency or have I set things up incorrectly?

Thanks.