"Both passwords must match"

Hi, I am attempting to set my account password using a password manager (the PasswordMaker Firefox add-on, as it happens), but when I do I get the error "Both passwords must match." I don't think it is very likely that this is the actual cause of the error, as the password manager should be inserting the same string in both fields. I have also tried copying the password to the clipboard and pasting it into both fields, and got the same problem.

I suspect something else is actually wrong about the pwd and it happens to be tripping the wrong error reporting code. Any thoughts on what that might actually be?