I noted thison my old version, too. It looks like Delftship rounds its sine and cosine calculations... after a slight rotation, meanwhile we feed it with integer numbers.

One of the problem's origins may be that the control points are not on the cylinder surface (radius or diameter) but at the intersection of two tengents to the cylinder's surface. This requires a calculation... which must be rounded.

I side with you Ruedi, it's boring

... but I'm unsure there's a solution... except editing the points' coordinates after calculating them yourself... and when the cylinder must be drawn at an angle...