From the user's perspective, the circle that was originally drawn, which wasn't touched when adding a second circle to the sketch. If the original was deleted,

From the user's perspective, the circle that was originally drawn, which wasn't touched when adding a second circle to the sketch. If the original was deleted, then it's unclear (possibly assume the first replacement). IIRC (not testing now) FreeCAD already handles this example sensibly. You can add circles to the sketch and the chamfer stays put. If you delete the circle and add a new one, it appears on the new hole. But if you add a square instead, it moves to a random edge of the rectangular hole. The 'edge' of the rectangular hole is actually a loop of four edges, so this is understandable. Commercial software can fix some of these cases - I don't think the Freecad link branch can, but it does at least detect that the original geometry was deleted and raises an error asking you to reselect instead of allowing things to move around. And unrelated features downstream don't break. Not dissimilar UX to when I mess with something that Fusion can't handle, I say.