Customer changes the GUI/CLI password on the ProxySG, they then use the text connection feature within Management Center (MC) to see if they can still connect to the ProxySG, this will work with both the old and the new password.

MC does not cache the credentials but it does use a persistent session to the ProxySG. Therefore unless the ProxySG closes all open SSH sessions for that user/password that is changed, it will continue to work until the session expires or closes. 

A bug has been opened with development to have this behaviour modified