How to check?
- Set Rendered mode for 3d View
- Set "Blend Sky" and "Real Sky" flags for world.
Rotate view you will see right color blending from Horizon to Zenith color.
- Add environment texture
Rotate view and you will see incorrect texture mapping that is not correspond to color blending that was observed in previous step.
So I conclude that this is a bug.
This issue must be solved before the patch D1414 because BI behavior is the viewport target.
Alexander (Blend4Web Team)