I am trying to render a simple sphere using a semi-transparent material made out of a blend of a Coated Glossy and a semi-transparent Shiny Diffuse material. When I put a couple of colored lights inside the ball and render the scene, I always end up having black spots in the render result. The color of the spots is defined as -1.#INF0, suggesting that they are render bugs. I'm using Blender 2.76b together with Yafaray 2.1.1 on a Windows 7 X64 machine. I tried different versions of Yafaray (down to version 1.1.0, but they all seem to have asimilar issues.
I tried replacing the Coated Glossy material with a normal Glossy material, but that didn't resolve the issue. The black spots somtimes seem to appear in the first render pass, but sometimes they appear at the start of the second render pass.