Eagle can't draw all circle quadrants correctly.
This may be involved in many other internal workings as well.
Upper left arc quarter is always drawn correctly, upper right arc is always drawn differently, if you draw any half-circle arc, it will always be asymmetrical, even if you draw wires with round endings, the end is asymmetrical, everything circular is asymmetrical along the axis of symmetry, under any zoom, and that is wrong for many reasons. I spent hours trying to fix defective board outline because Eagle can't draw a circle.