During my tests while preparing the Material Preview with camera rotation I've found a bad problem in the world background.
There are two different issues happening, when using a background image texture:
* Artifacts in the image: I used a black texture with a yellow circle on it and when rendering the yellow circle has strange black artifacts.
* Incorrect IBL light position. This is bad: when using a background image texture in Angular mode and enablign IBL, the light from the IBL is in a DIFFERENT position respect to the texture! This would cause the illumination in the scene NOT MATCHING the background texture!
I've checked with older YafaRay versions and both problems also happen. So, this seems to be a very old problem that for some reason went unnoticed?
I've attached an example (and very simple) blend file showing this problem. Please unpack the jpg texture before rendering.