I have detected a difference between v4 and v5 that may catch you out. Going
forward, v6 may be different to v5.
When a polygon is defined using a wire with curvature, Eagle converts that
wire to a series of straight wires (contour).
I have discovered that v4 and v5 seem to do the conversion differently and
you can end up with a different set of contour wires in each version for the
same wire with curvature.
In one of my examples v4 gives 19 wire segments and v5 gives 20, for the
same wire with curvature.
Warren