The semicolons did not replace any letters, they were a surprising addition. The number of letters in my password did not change (I watched), so I assume there were no added semicolons there. And, even without them, I could not log in: I had to hit the "cookie jar" before I typed in both the name and the password.
As a matter of fact, I don't have that log in problem any more. It is gone without any action on my part. Mystery. Probably a glitch? Oh well.
