Just seeing if there's been any progress on this, because it's _really_ slowing my modeling down and I'm hoping it won't be a problem in the final release.

OK, just tried the beta available at this time on Blender.org (2018-12-19-22:13, c4ee77cde8d0), and the problem still exists.

OK, just to be more clear before trying a newer beta. If you select, well, anything, and then want to deselect an edge loop, if you are in 3 button emulation mode, it simply won't happen. No mouseclicks or key combinations will deselect an edge loop. There is nothing you can do. If you aren't in 3 button emulation mode, Shift+Alt+click will deselect an edge loop.

Thanks so very much for the information! And a double thanks for responding so quickly when you're so very busy. Just to let you know, I don't think it's known in the community, because I searched on this topic and found nothing but people blaming the artist for making mistakes with their maps or shaders. I also asked about it and had someone suggest that I post a bug report. I wasn't trying to needle you or anything. I wouldn't have bothered you at all if I'd realized that you were already aware of the issue.