My recent experiments:
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In Quickslice/Standard/

open calcyl.stl
scale ( 2  2  0.2 )
move ( -0.6  -0.6  0 )

open calbox.stl

{==> this will superpose the two shapes and produce a cylinder with a square hole}

slice

{==> this gives a set of curves with which you can now do experiments}

On any individual level I tried:

1.)
build roads ==> solid fill of outer ring only.
:-(

2.)
select inner curve; 
edit curve/advanced/copy in_x_y/copy with offset (0.01, 0.01);
select one of the two inner curves; add to light magenta set; 
build roads ==> now I get solid fill of outer ring, 
and loose fill of slightly offset square hole.

3.)
select shifted square curve, and move on top of other square;
build roads ==> we still get a solid fill of outer ring, 
and loose filling of square hole.
:)

A more direct path to success:

4.)
starting from original state in bullet 1.)
select inner curve; add to light magenta set; 
build roads ==> still only get outer ring filled.
:-(

5.)
select inner curve; edit curve/advanced/copy in_x_y/copy with offset (0.0, 0.0);
build roads ==> now I get solid fill of outer ring, and loose fill of square hole.
:)

PS.
If you do your work on the machines in 349, and want to save any files,
you have to click the "Options" button in the "Save As" menu, 
and uncheck gzip STL file and gzip SSL file.  
{The problem is apparrently because gzip is not installed on those computers.}

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