Shape tools pixel size is ignored if filled

When you use the shape tools, choose a brush size and use whatever shape you want, you can either get sharp or round corners, but if you tick 'Filled' then the size will reset back to 1 regardless of the shape you're using, this means that you can't directly make filled shapes with round corners.

How to reproduce:
1. choose Rectangle tool and set shape to ellipse
2. set brush size to 10 or something, the size doesn't matter as long as you can see the shape being rounded.
3. tick the 'filled' button

Expected result:
The shape will become filled and the corners will be rounded 

Actual result:
The shape is being filled and the corners sharp.