I tried to create two degenerated paths (really close points), as follow:

Code :
path4 = vgCreatePath(VG_PATH_FORMAT_STANDARD, VG_PATH_DATATYPE_F, 1.0f, 0.0f, 0, 0, VG_PATH_CAPABILITY_ALL);
pathSegs[0] = VG_MOVE_TO_ABS;
pathData[0] = -0.00005f;
pathData[1] = -0.00005f;
pathSegs[1] = VG_CUBIC_TO_ABS;
pathData[2] = +0.0001f;
pathData[3] = +0.0001f;
pathData[4] = -0.0001f;
pathData[5] = +0.0001f;
pathData[6] = +0.00005f;
pathData[7] = -0.00005f;
vgAppendPathData(path4, 2, pathSegs, pathData);

Code :
// NB: path5 should be the result from a path4 flattening. Code has been taken from Reference Implementation
path5 = vgCreatePath(VG_PATH_FORMAT_STANDARD, VG_PATH_DATATYPE_F, 1.0f, 0.0f, 0, 0, VG_PATH_CAPABILITY_ALL);
j = 0;
for (i = 0; i < 256; ++i) {
	float p0x = -0.00005f;
	float p0y = -0.00005f;
	float p1x = +0.0001f;
	float p1y = +0.0001f;
	float p2x = -0.0001f;
	float p2y = +0.0001f;
	float p3x = +0.00005f;
	float p3y = -0.00005f;
	float t = (float)i / 255.0f;
	float u = 1.0f - t;
	pathData[j++] = u * u * u * p0x + 3.0f * t * u * u * p1x + 3.0f * t * t * u * p2x + t * t * t * p3x;
	pathData[j++] = u * u * u * p0y + 3.0f * t * u * u * p1y + 3.0f * t * t * u * p2y + t * t * t * p3y;
}
vguPolygon(path5, pathData, j / 2, VG_FALSE);

And then I've drawn them (using a large stroke line width) with the following code:

Code :
vgSetfv(VG_STROKE_DASH_PATTERN, 0, NULL);
vgSetf(VG_STROKE_LINE_WIDTH, 126.0f);
vgSeti(VG_STROKE_CAP_STYLE, VG_CAP_BUTT);
vgSeti(VG_STROKE_JOIN_STYLE, VG_JOIN_ROUND);
vgClear(0, 0, 256, 256);
vgSeti(VG_MATRIX_MODE, VG_MATRIX_PATH_USER_TO_SURFACE);		
vgLoadIdentity();
vgTranslate(64.0f, 128.0f);
vgDrawPath(path4, VG_STROKE_PATH);
vgLoadIdentity();
vgTranslate(192.0f, 128.0f);
vgDrawPath(path5, VG_STROKE_PATH);

Because path5 should reproduce the path4 flattening (I've taken the code directly from the public Reference Implementation), and given that I've used round joins to simulate the smooth connection of the cubic curve, I would expect to see two similar drawings, instead of the following result:



Could someone explain the reason of this different behavior?
Thanks in advance.