Win7pro 32bit Qcad 3.23.0

Andrew,
The Arc segments of Polylines with Global or any Local Width render faulty where Global Z or any of the arc's local Z is not zero.

In the attached drawing setting the Global Z of the inner poly to 5,10,...

The setting of Z to not zero affects the radius of the projected arc and not the bulging of the poly.
It also affects the projected widths of the line inversely, but not by changing the widths properties.

Pritty rare combination! True.
Qcad is 2D native! True.

Flatten will resolve this.

It is not a purely visual rendering fault, the poly will explode as such.

Maybe similar flaw as with uneven scaling blocks with arcs.
https://qcad.org/rsforum/viewtopic.php?f=8&t=5566#p20703

Regards