Shooting an arrow prints "added speed" in the Game Output

Shooting an arrow prints the following into the Game Output:

added speed 0.0, 0.0, 0.0

(values may vary)

The code causing this can be found in the decompiled version of Minecraft 15w51b in the zs.java class:

public void a(rp rp2, float f2, float f3, float f4, float f5, float f6) {
	float f7 = (- om.a(f3 * 0.017453292f)) * om.b(f2 * 0.017453292f);
	float f8 = - om.a(f2 * 0.017453292f);
	float f9 = om.b(f3 * 0.017453292f) * om.b(f2 * 0.017453292f);
	this.c(f7, f8, f9, f5, f6);
	this.r += rp2.r;
	this.t += rp2.t;
	if (!rp2.y) {
		this.s += rp2.s;
	}
	System.out.println("added speed " + rp2.r + ", " + rp2.s + ", " + rp2.t);
}