This page demonstrates how, after applying a custom THREE.ShaderMaterial to a model in the Forge viewer (version 7.90.0), the following bugs are noticed:

1. Group selection does not work correctly (Ctrl+Left Click and drag). Almost 100% of the time, the meshes you attempted to select will not be selected. click to view screenshot

2. Hovering over a particular mesh with the cursor will sometimes highlight completely different meshes in the scene. click to view screenshot

3. Selecting a single mesh will cause what appears to be Z-fighting/stitching between the ShaderMaterial and the selection material. How could this happen on a single mesh? Note: the Selection Mode must be set to "Leaf Object" or "Last Object" to trigger the Z-fighting. click to view screenshot

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to activate the bugs.