Why does the denominator of TF change in MATLAB when multiplying by proportional gain?

Hi everybody, Trying to simulate a unity feedback closed loop system with gain of K

Let's say I want a system:

 K = 5 ;
s = tf('s');
G = 10/(s^2+2*s+1);
sysCL = feedback(K*G,1);

The script returns:

sysCL =

          50
    --------------
    s^2 + 2 s + 51

Am I missing something here? I thought K*G the denominator would be (s^2 + 2*s +1). I'm just starting out in my design controls systems course.