I just tried it for you. It allows you to reuse your old password.
What I did
I logged in under my current password.
I went to account page and changed my password.
I logged out.
I shut down my browser.
I started up my browser.
I went to Auctiva and tried to log in with my old password. Not accepted. This confirmed that I actually changed the password.
I logged in with the new password.
I logged in and out again to make sure the new password worked for at least two logins.
I changed the new password back to my previous one and logged in again. I repeated it to make sure my old password worked again.
So it appears Auctiva passwords can be reused if you want to make a temporary change.
However it is good practice to change them regularly as you probably already know. Hard to do when most people have so many accounts.