GUI button2d changes opacity when close or behind object

We have an house exported from blender and added some 2d gui buttons to the scene to interact with the object and link the user to a subsite.
The problem is when you rotate the object via arc camera the opacity of the buttons change when they are close or partialy behind the object (see video Imgur: The magic of the Internet). I tried to reproduce it here but it is not the same behavior as in my example. https://playground.babylonjs.com/#MHKKUX#2
Following is how i add the button to the scene:

const plane = BABYLON.MeshBuilder.CreatePlane('btn-label-' + alias, { size: 5 }, scene);
const advancedTexture = GUI.AdvancedDynamicTexture.CreateForMesh(plane);
const button = GUI.Button.CreateImageOnlyButton('but', '/house3d/textures/target.png');
plane.position = new BABYLON.Vector3(posX, posY, posZ);
plane.billboardMode = BABYLON.TransformNode.BILLBOARDMODE_ALL;
button.width = 1;
button.height = 1;
button.thickness = 0;
advancedTexture.addControl(button);

I think the mesh material should have something like useSpecularOverAlpha = false ?