decsg ignores a shape

I use decsg to iteratively create a simple geometry representing a circle minus a polygon, where circle is constant and the polygon changes from one iteration to another. At each iteration I have:

O = [1, 0, 0, 2]'; % A circle with the centre at (0,0) and radius 2
n = size(PolyCoord,1); % PolyCoord is a n-by-2 array with the x- and y-coordinates of the polygon's points
P = [2, n, PolyCoord(:,1)',PolyCoord(:,2)']'; % Polygon
O = [O; zeros(length(I) - length(O),1)]; % Additional zeros

gm = [O,I];
sf = 'O-I';
ns = char('O','I')';
g  = decsg(gm,sf,ns); % Generate geometry

I run this code for different PolyCoord, but O is always the same. However, for some reason, O is sometimes ignored, and g represents just the polygon P. The polygon is always inside the circle, the matrices consisteny is checked.

A slight change of the centre's coordinates can help:

eps = 1e-2;
O = [1, eps, eps, 2]';

However, is there a more systematic solution to this problem?