Core Image filter kernel function crashes

gistfile1.glsl

/*
 * I'm trying to write Core Image filter kernel functions in Quartz Composer,
 * but it's crashing consistently on certain pieces of code that should be fine.
 */
 
// This works fine:
kernel vec4 coreImageKernel(sampler image, __color color1) {
  vec4 inputColor = sample(image, samplerCoord(image));
  return inputColor;
}

// And this works fine:
kernel vec4 coreImageKernel(sampler image, __color color1) {
  return color1;
}

// But this crashes every time:
kernel vec4 coreImageKernel(sampler image, __color color1) {
  vec4 inputColor = sample(image, samplerCoord(image));
  return color1;
}

// This works fine:
kernel vec4 coreImageKernel(sampler image, __color color1) {
  vec4 inputColor = sample(image, samplerCoord(image));
  return color1 + inputColor * 0.0000000001;
}

// But this crashes:
kernel vec4 coreImageKernel(sampler image, __color color1) {
  vec4 inputColor = sample(image, samplerCoord(image));
  return color1 + inputColor * 0.000000000;
}

/*
 * The crash is a SIGABORT "pointer being freed was not allocated" in
 * com.apple.CoreImage FEApplyTreeNode::render2(...).
 * 
 * How can that be? Is there something important I'm missing about how to write
 * OpenGL shader functions for Core Image kernels? Or is Core Image / Quartz
 * Composer just really buggy?
 */