Not so much a bug, but just unexpected behavior
On the GUI Ellipse Element, Shadows will NOT render unless a background color is set (not shadow color, but actual background color).
Would be nice to make “open” circles with a shadow, but right now not possible.
Looking into the code, it looks like it is actually by design and I am afraid of introducing regressions by changing it. If you are not in a hurry I guess we should wait next monday to take advices from @Deltakosh on this one. I feel bad to not take the decision but Gui is definitely his baby