Problems ellipse gradient and overprint

Dear all,

I've some problems with a ellipse which is colored with an gradient. (1 spot color)

I want to change the ellipse to overprint (attributes / overprint fill).

After this change the aspect ratio will also be changed, I don't know why ?

It seems that the value will be multiply by 2,520775623269. Why?

The ellipse is a delivered file.

If I create a new shape by my own there is no problem with the settings.

Please see example below:

It would be great if anyone could help here.

Thank you and best regards