32bit Tangent VDMs exported from Zbrush. Either baked from a sculpt, or the diagnosis tool they have built in. Tangent FlipnSwitch set to 43.

If I place the VDM into displacement slot of the material editor tab, and select Vertex Displacement; it will then freeze on me before crashing.

Only after opening it up in a photo editor and attaching an alpha channel to the image will CC4 read the file correctly, even though the alpha channel has zero data in it.