Presumably this is because the shadowed area is behind the shapes and transparency would reveal that (eg on the circle)

I had a fiddle around in the shapesheet of a couple of these shapes and didn't have much luck in removing the transparency but I did find a relatively easy way to make a shape transparent via the Styles.

If you edit the Fill attributes of the style "Block Normal" to make it transparent then you can (re)apply that style to your shapes and they will become transparent.

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Andrew Lockton
Chrysalis Design, Melbourne Australia