hlsl nointerpolation behaviour - graphics

Question

For an experiment I want to pass all edges of a triangle to the pixel shader and manually calculate the pixel position with the triangle edges and bayrcentric coodinates.
In order to do this I wrote a geometry shader that passes all edges of my triangle to the pixel shader:
struct GeoIn
{
float4 projPos : SV_POSITION;
float3 position : POSITION;
};
struct GeoOut
{
float4 projPos : SV_POSITION;
float3 position : POSITION;
float3 p[3] : TRIPOS;
};
[maxvertexcount(3)]
void main(triangle GeoIn i[3], inout TriangleStream<GeoOut> OutputStream)
{
GeoOut o;
// add triangle data
for(uint idx = 0; idx < 3; ++idx)
{
o.p[idx] = i[idx].position;
}
// generate verices
for(idx = 0; idx < 3; ++idx)
{
o.projPos = i[idx].projPos;
o.position = i[idx].position;
OutputStream.Append(o);
}
OutputStream.RestartStrip();
}
The pixel shader outputs the manually reconstructed position:
struct PixelIn
{
float4 projPos : SV_POSITION;
float3 position : POSITION;
float3 p[3] : TRIPOS;
float3 bayr : SV_Barycentrics;
};
float4 main(PixelIn i) : SV_TARGET
{
float3 pos = i.bayr.x * i.p[0] + i.bayr.y * i.p[1] + i.bayr.z * i.p[2];
return float4(abs(pos), 1.0);
}
And I get the following (expected) result:
However, when I modify my PixelIn struct by adding nointerpolation to p[3]:
struct PixelIn
{
...
nointerpolation float3 p[3] : TRIPOS;
};
I get:
I did not expect a different result because I am not changing the values of p[] for a single triangle in the geometry shader. I tried debugging it by changing the output to float4(abs(i.p[0]), 1.0); with and without interpolation. Without nointerpolation the values of p[] do not vary within a triangle (which makes sense, because all should have the same value). With nointerpolation the values of p[] do change slightly. Why is that the case? I thought nointerpolate was not supposed to interpolate anything.
Edit:
This is the wireframe of my geometry: