Baked lightmap is full of artifacts

I am having a very strange problem with an imported FBX model. If I place the lights in the model everything is ok but when I bake them the resulting lightmap is severely artifacted exposing the polygon lines. I have included two images below.

No baked lights:

With baked lightmap:

As you can see this just doesn't work. The lights are simple point lights placed close to the ceiling. They are set to "no shadows" and "bake only". Everything else is default (color white, intensity 1). I am not doing anything special like ambient oclusion.

I haven't encountered anything like this while searching the answers here or on the forums.