Wrapping with Opacity widget makes it work broken

Hi, love this package!

However, I've encountered a bug. I'm using it as border of a MaterialButton.

> MaterialButton(
> elevation: 0,
> shape: SmoothRectangleBorder(
> side: BorderSide(color: Colors.white, width: 4),
> borderRadius: SmoothBorderRadius(
> cornerRadius: 16,
> cornerSmoothing: 1.0,
> ),
> ),
> color: lightestColor.withOpacity(0.3)...

When I wrap it with Opacity widget, there is an error on the corners as following photo shows. (Bottom one is wrapped with Opacity) (Even if the opacity is given as "0.99", it happens.)