What I would do is convert the spline to polyline and then use the Circle 3pt command to create the circle and be done with it. You may be wasting time trying figure out a fix where there may not be one. HTH.
I used flatten on a spline which converted it to a pline with just the right amount of arc segments. I exploded the pline and was left with nice arcs and not the multitude of arcs splinedit gives when converting to pline.
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