Why "Warning X4000: use of potentially uninitialized variable" shows for more than one usage of common method?

I have a common method in hlsli

/// RendererShaderTypes.hlsli
///
static inline float4 OverlayColor(float2 texOverlay, float4 videoColor)
{

      float4 texColor = float4(imageMixTexture[4].Sample(imageMixSampler[4], texOverlay));
      if (texColor.r == keyColor.r &&
          texColor.g == keyColor.g &&
          texColor.b == keyColor.b)
      {
          return videoColor;
      }
      return lerp(texColor, videoColor, transparency);
}

It's called from more than one hlsl pixel shaders.

#include "RendererShaderTypes.hlsli"
float4 main(PSPosTexOverlay input) : SV_TARGET
{
    return OverlayColor(input.texOverlay, backColor);
}

also called to another pixel shader

#include "RendererShaderTypes.hlsli"
float4 main(PSPosVideoTexture input) : SV_TARGET
{
     // lookup color of video
     float4 mixColor = mul(colorMatrix[0], VideoColor(imageMixSampler[0], imageMixTexture[0], input.texImage));
     mixColor.rgb *= mixColor.a;
     mixColor.a = 1.0f;
     return OverlayColor(input.texOverlay, mixColor);
}

when compiled shows following warning. Any idea why it's showing?

warning X4000: use of potentially uninitialized variable (OverlayColor)

I don't know yet any satisfactory reason but I have solved the issue. Any function that calls a mid-function return statement will show the warning during compilation. I have re-writed one of above like this and the warning went away.

static inline float4 OverlayColor(int texIndex, float2 texOverlay, float4 videoColor)
{
    float4 texColor = float4(imageMixTexture[4].Sample(imageMixSampler[4], texOverlay));
    float4 overlayColor;
    if (texColor.r == keyColor.r &&
        texColor.g == keyColor.g &&
        texColor.b == keyColor.b)
    {
        overlayColor = videoColor;
    }
    else
        overlayColor = lerp(texColor, videoColor, transparency);
    return overlayColor;
}