Geometry shader odd issue

Question

I want to use geometry shader to draw triangles of mesh, but encounter a really odd issue.

Result As follow: The wrong output.

The Right output.

The only diff between wrong and right in code, is when converting 3d position vector to 4d position vector. The right one did in vertex shader. The wrong one did in geometry shader.

Code as follow. Why this happend?

#version 330 core

layout (location = 0) in vec3 pos;
layout (location = 1) in vec3 normal;

uniform mat4 model;
uniform mat4 view;
uniform mat4 project;

out vec3 normal_;
out vec4 pos_;
out vec3 pos_bug_;
out mat4 mvp_;

void main()
{
  mvp_ = project * view * model;
  normal_ = normal;
  pos_ = vec4(pos, 1.0);
  pos_bug_ = pos;
}

#version 330 core

layout (triangles) in;
layout (line_strip, max_vertices = 12) out;

uniform float length = 0.4f;

out vec4 color;

in mat4 mvp_[];
in vec3 normal_[];
in vec4 pos_[];
in vec3 pos_bug_[];

void GenNormal(int index) {
  color = vec4(1, 1, 0, 1);
  gl_Position = mvp_[0] * pos_[index];
  EmitVertex();
  gl_Position = mvp_[0] * pos_[index] + vec4(normal_[index], 0.0) * length;
  EmitVertex();
  EndPrimitive();
}

void GenTriangle(int index0, int index1) {
  color = vec4(1, 1, 1, 1);
  gl_Position = mvp_[0] * pos_[index0];                   // Right
  // gl_Position = mvp_[0] * vec4(pos_bug_[index0], 1.0); // Wrong
  EmitVertex();
  gl_Position = mvp_[0] * pos_[index1];                   // Right
  // gl_Position = mvp_[0] * vec4(pos_bug_[index1], 1.0); // Wrong
  EmitVertex();
  EndPrimitive();
}

void main()
{
  GenNormal(0);
  GenNormal(1);
  GenNormal(2);
  GenTriangle(0, 1);
  GenTriangle(1, 2);
  GenTriangle(0, 2);
}