Here is a post from the bobcad forum by the Bird BCC tech. man
Believe it or not, the crop circles that most people get are due to the geometry used to generate the toolpath.
What happens is when you have an arc and a line that intersect and the line is not perfectly tangent to the arc, the system generates an arc move around the corner. This arc can be so small that the beginning and end of the arc have a difference that is less than 0.00005, so when the coordinates are rounded you get the same position for both the end of the arc and the beginning of the arc (full circle).
I suggest trying to use the Make Arcs Tangential command, when possible. That alone should help reduce the appearance of the arcs.
Regards