Shape keys distort mesh in unexpected ways

If you 'fast preview' the enclosed blend with 'export shape keys' turned off for cube.001, it behaves as I would expect.

With 'export shape keys' turned on however, the shape key ' Big' works just fine, but all sorts of extra curves and distortions appear on the faces of the mesh. Any idea why and what I can do to stop it? All that _should_ happen is that the shape key adjusts the diameter of the hole.
TIA Phil Robinson

With 'export shape keys' turned on however, the shape key ' Big' works just fine, but all sorts of extra curves and distortions appear on the faces of the mesh.

Yes, it's appear because shape keys work only with smooth shading mode of an object, but you use flat shading in blender and when you exporting model with "export_shape_keys" to the engine it applies smooth shading automaticaly. So, the solution for you will be to divide each face on your model by hands where it needed with smooth shading on the model and then create shape keys for it.

That was fast, thanks.

Like this you mean?
I've put some loop cuts around the hole, and that does constrain the weirdness to the area between the hole and the loop cuts, but it's still there and very visible.

I think maybe I didn't understand you right?
Thanks again, Phil Robinson

Like this you mean?

Not exactly. I mean something like this shapekey-distortion-demo.blend. I just separated some faces using Enge Split Modifier before I add shape keys to the object.

Thanks Mikhail; I finally got around to trying this and it works! Can't say I understand it but I'm used to that! Thanks again, Phil

Incidentally, if you want to have perfect English, your sig should really be
"Blend4web and that kind of thing"
or
"Blend4web and those kinds of things"
because 'that' is singular, but 'things' is plural.
Hope it helps - Thanks again, Cheers, Phil

Incidentally, if you want to have perfect English, your sig should really be
"Blend4web and that kind of thing"
or
"Blend4web and those kinds of things"
because 'that' is singular, but 'things' is plural.
Hope it helps - Thanks again, Cheers, Phil

Thanks, it's really helpful.