Hi Narater,
In the images from my post above I detail what I changed. I took the original UV you had and applied that to the second UV channel. I then looked to see what UV faces were overlapping. The only parts overlapping were the pieces I removed and stuck in the top right and left corners. This was a simple way for me to check and see if the lightmap was the main culprit to the lightbleed. Since the mesh wasn’t being broken up as it is in the image you’ve posted it didn’t allow lightbleed to be baked into the texture.
Lightmap are used to bake lighting into a texture for anything that is static (non-movable). This gives no overhead for the object at run-time with shadows.
If your object is set to Movable it will not need a lightmap because the shadows are not being baked into a texture since the shadows are dynamically created based on the object.