In the context of his post, I also do not think that a new thread is need for this. But generally speaking I have seen people hunting other users because of password change. Whenever there is a password change or an email change, they'll immediately allege that it is an account changing hands.
Changing the password is the right of every user and it should not be taken as a negative thing. However, if any user changes his password, and then we see his posting habits changed considerably then there might be a possibility that the account changed hands or the account might be sold.
Anyways, for a genuine user, this may never be a problem as the original owner of the account can always sign a message with an old address and satisfy everyone that there is no change in the ownership of the account.