Setting segment opacity to < 1.0 hides segments

@chir.set Hi, after looking into your issue, I noticed an interesting similarity with a problem I’m experiencing on Linux.

When I set the segmentation opacity to anything below 1.0, the rendering also becomes incorrect. In your case, the segmentation disappears completely, while in my case it becomes fragmented/corrupted.

The symptoms are different, but both problems seem to start when the opacity goes below 1.0. Could you take a look and see if you can guess what might be happening in both cases, and whether they could be related somehow?
Link to my issue: Color display error on 3D Volume