editing conic in sketch disrupts associativeness

I have a conic in the sketch "S1:Conic". When its Rho is changed from 0.5 to 0.4, an alerting message shows up. After exitting the Sketch Task Environment, a CSYS associated with it moves unexpectedly!

What should I do to keep the CSYS (green) where it was? Thanks!

• "S1:Conic" = blue curve: A Conic (Rho=0.5) in sketch S1.

• "Scaled" = black curve: The conic is scaled up with simple factors.

• "CSYS_1" = green CSYS: The orgin lies at the end point of the Black curve, axes following CSYS_absolute.

Fig.1 At the beginning, Rho of "S1:Conic" is 0.5.Fig.2 Changing "S1:Conic" Rho from 0.5 to 0.4.Fig.3 After quiting the sketch task environment, the green CSYS moved unexpectedly!