I'm not really sure what the issue is, it looks like you're getting the result I'd expect? If you want the padding to extend further, increase it from 10.
Hello guys, i try to bake LightMap to simple object. I'm using for tests mesh with uv and one standart light. Mental ray as a renderer. In the 'Render to texture' i set Padding = 10. But padding crashed into black. Here pictures...