Windows 10 LTSB, GTX 970 & GTX 960
Short description of error
When trying to change the environment texture to any texture, even just a solid color, the texture does not change from what it was at launch time of the blend file.
Exact steps for others to reproduce the error
Download the broken version from the screenshot above, make or open a scene, and then try to change the environment texture, it will stay as it was at launch time.