The system does not correctly calculate the CDF of a Binomial using the Regularized Incomplete Beta for p=0.5.

restart;
n := 10;
f := x -> int(t^(n - x - 1)*(1 - t)^x, t = 0 .. 1 - p)/Beta(n - x, x + 1);
p := 0.5;
plot(f(x), x = 0 .. 10);