OpenGL layered rendering interferes with layer 0

Question

I am using gl_Layer = gl_InvocationID; in a geometry shader to render into a framebuffer with a 3D texture attached.

This mostly works fine. Except every invocation of the shader also renders into layer 0, as well as the layer that I specify.

How can I avoid this? Is there something vital I'm missing with setting up the framebuffer? Perhaps with glFramebufferTexture?

Geometry Shader

#version 400

layout(invocations = 32) in;
layout(points) in;
layout(triangle_strip, max_vertices = 3) out;

out vec3 raster_color;

float blue;

void main()
{
  gl_Layer = gl_InvocationID;
  blue = float(gl_InvocationID) / 31.0;

  gl_Position  = vec4( -1.0, -1.0, 0.0, 1.0 );
  raster_color = vec3( 0.0, 0.0, blue );
  EmitVertex();

  gl_Position  = vec4( 1.0, -1.0, 0.0, 1.0 );
  raster_color = vec3( 1.0, 0.0, blue );
  EmitVertex();

  gl_Position  = vec4( 0.0, 1.0, 0.0, 1.0 );
  raster_color = vec3( 1.0, 1.0, blue );
  EmitVertex();

  EndPrimitive();
}

Fragment Shader

#version 400

in vec3 raster_color;
out vec4 fragment_color;

void main()
{
  fragment_color = vec4( raster_color, 1.0 );
}

Answer 1

Turned out it was not a problem with gl_Layer. It was simply a syntax error in glTexParameter that was causing my resulting 3D texture to repeat rather than clamp to edges.