There was this thread about it in the past. I have such problem with some of my added fonts too. I thought it settled with PC restart, but its still there. To me these fonts do not obey opacity setting, even when I try to set it directly with slider, not only by expressions. The one that is not working for you, works well for me. Did not try it on watch yet.
I tried to check the opacity in the .gwd file it self, but could not find it in the contained .xml files. I wonder where it hides.
