In that example I used zero infill, but I've experimented with different density values - got the same result.
100% threshold in not ok as well because it causes another issue... hmmm... For that particuar cube, if I use 3 bottom skin layers then set bridging support threshold = 100% it happens that first 2 layers appear normal but the 3d one becomes bridge-styled. It seems like Cura detects that the 1st layer is like 100% solid but the 2d one is not. So, it draws 3d layer as a bridge over that.
I'm not sure if I described that issue correctly. There are too many things