Strange offset2D result

Any idea why offset2D gives different results for these two test blocks?

```
import cadquery as cq

test1 = (cq.Workplane()
.box(25,25,1)
.faces(">Z").workplane()
.moveTo(7.825,-3.155)
.circle(3.15/2).cutThruAll()
.moveTo(-7.825,-3.155)
.circle(3.15/2).cutThruAll()
.moveTo(-7.825,3.155)
.circle(3.15/2).cutThruAll()
.moveTo(7.825,3.155)
.circle(3.15/2).cutThruAll()
)

test2 = (cq.Workplane()
.box(25,25,1)
.faces(">Z").workplane()
.rect(2*7.825,2*3.155,forConstruction=True)
.vertices().circle(3.15/2).cutThruAll()
)

circles1 = test1.faces(">Z").edges("%CIRCLE")
small_circles1 = circles1.toPending().offset2D(-0.5)
# same as test1, but shifted up by 2 for viewing
circles2 = test2.translate([0,0,2]).faces(">Z").edges("%CIRCLE")
small_circles2 = circles2.toPending().offset2D(-0.5)

show_object(circles1,options={"color":"blue"})
show_object(small_circles1,options={"color":"red"})

show_object(circles2,options={"color":"orange"})
show_object(small_circles2,options={"color":"yellow"})

```

For test1 (red/blue) the offset is correct for the circle at the last 'moveTo' position (shuffle the order of the moveTo lines and the last one will have the proper offset)..

I also saw a case where the circles were sized properly, but their locations were shifted in X, Y and Z from where they were expected. There are two other issues ( [#896](https://github.com/CadQuery/cadquery/issues/896) and [#753](https://github.com/CadQuery/cadquery/issues/753)) already open that sounded like they are related to that issue.