FX files and fixed-function parameters

It seems to me as if the fixed-function parameters (such as light direction) get baked when you first load the effect, whereas the same parameter for shaders gets updated correctly. If I have

float3 CamPos : CAMPOS = { 0, 0, 0 };

technique t0 {
  pass p0 {
    LightPosition[0]  = (CamPos);
    ...
    VertexShader = NULL;
  }
}

technique t1 {
  pass p0 {
    VertexShader = compile vs_1_1 VS();
  }
}
 

and VS() references CamPos, then the t1 technique will do the right thing as I update the CAMPOS semantic, but the t0 will "bake" the light position at whatever the camera position was when I started. What is the appropriate fix for this? Could I tag the LightPosition[0] argument using : CAMPOS semantic? Is this a known bug or limitation? Something I could be doing wrong that I could change?