Comment 7 for bug 171531

Correction: scour is not faulty at all.

Scour just removes an unnecessary fill-opacity: 1; attribute in a path element.
But when this path is linked in a use element later, this removal causes Inkscape to multiply an opacity element and a fill-opacity element, and thus apply an almost zero value. In the original (non scoured) tutorial, the use element seems to inherit the fill-opacity attribute (1) from the path element, and thus the overall opacity is equal to the opacity attribute only.

Non scoured path element:
<path style="fill:#ffffff;fill-opacity:1; ....... id="path1508" />

Soured path element:
<path style="fill:#ffffff; ........ id="path1508" />

use element:
<use style="opacity:0.084269650;color:#000000;fill:#ffffff;fill-opacity:0.064615376; ...... xlink:href="#path1508" />

Possible workarounds:
1. Set the path's fill-opacity element to 0.9999 (a bit dirty, isn't it?) so that it is not removed by scour.
2. Remove the opacity attribute in the use element.

I think I'll use workaround #2.