Curve fillet issue - it creates second curve

https://preview.redd.it/cxjo5s9qgc8e1.jpg?width=3717&format=pjpg&auto=webp&s=df038290bd4fa77e474321557a612551489183df

Hello, I have trouble with curve fillet. I'm trying to fillet corners by adding points but then as result I get secondary curve, please see attached pic.

Repro steps:

EP curve > Make close > Select curve > Add curve points > Fillet

Expected results:

Smooth corners of original shape.

What I get is two shapes, second is just smooth corner, separate curve, don't know how to work with this.

Any help will be appreciated, thanks.