Why the width of the green line of pattern named "c" is greater than "b" although all of them are 0.5bp?

[justonlyasy]

My code,

settings.outformat="pdf";
import patterns;
picture sixpointedstars(pen fillpen=currentpen,pen drawpen=currentpen)
{
picture tiling;
path g=polygon(6);
pair[] A;
for (int i=0;i<6;++i) A.push(reflect(point(g,i),point(g,i+1))*(0,0));
filldraw(tiling,point(g,0)--A[0]--point(g,1)--A[1]--point(g,2)--A[2]--
point(g,3)--A[3]--point(g,4)--A[4]--point(g,5)--A[5]--cycle,fillpen,drawpen);
return tiling;
}

size(10cm);

add("b",scale(8)*sixpointedstars(red,green+0.5bp),(3,3),(3,3));
add("c",scale(8)*sixpointedstars(red,green+0.5bp),(1,1),(1,1));

filldraw(unitcircle,pattern("b"),black+0.5bp);
filldraw(shift(3,0)*scale(2)*shift(-0.5,-0.5)*unitsquare,pattern("b"),black+0.5bp);

filldraw(shift(0,-3)*unitcircle,pattern("c"),black+0.5bp);
filldraw(shift(0,-3)*shift(3,0)*scale(2)*shift(-0.5,-0.5)*unitsquare,pattern("c"),black+0.5bp);

shipout(bbox(2mm,Fill(white)));

How to get the same width of the green line for both?

[johncbowman]

For the record, here's a more minimal example that shows something is definitely wrong with patterns (using gs 9.55.0):

settings.outformat="pdf";
import patterns;
picture sixpointedstars(pen drawpen=currentpen)
{
picture tiling;
path g=polygon(6);
pair[] A;
for(int i=0; i<6; ++i) A.push(reflect(point(g,i),point(g,i+1))*(0,0));
draw(tiling,point(g,0)--A[0]--point(g,1)--A[1]--point(g,2)--A[2]--
point(g,3)--A[3]--point(g,4)--A[4]--point(g,5)--A[5]--cycle,drawpen);
return tiling;
}

add("b",sixpointedstars(green));
add("c",sixpointedstars(green));

path g=scale(20)*shift(-0.5,-0.5)*unitsquare;

filldraw(shift(30,0)*g,pattern("b"));
filldraw(g,pattern("c"));