They also did that at one of my previous workplace. We couldn't reuse any of the passwords we used in the past (no limit apparently), but in the form to change

They also did that at one of my previous workplace. We couldn't reuse any of the passwords we used in the past (no limit apparently), but in the form to change our password, they checked if the current and new passwords were different w/ some Js. With the help of firebug we could keep the same password as long as we wanted.