fintersect() does not preserve order

[mllg]

x1 = c("b", "c", "a")
x2 = c("a", "c")

intersect(x1, x2)
fintersect(data.table(x = x1), data.table(x = x2))$x

The result is ordered according to the 2nd argument while R's intersect() preserves the order of the first argument.