Flatten Doesn't Work if Pencil Has Different Thickness (Size)

Hi,

I have an issue with Flatten on Pencil Lines (on Windows 8 )

The Auto Flatten and Flatten from Optimization menu/Select toolbar does not work if the Pencil Lines has different thickness or size

In the screenshot, you can see that I have two pencil lines. The thick one for eyelash and the thin one for eyeball.
I try to Flatten them, it just doesn’t work.

The Flatten only works with Brush stroke. I tried to convert it to brush stroke and have it flattened but when I convert it back to pencil line, it becomes messy.

Thanks!

Donny

…Oo… nevermind