Hi,
i too found this strange behaviour by accident.
My wordpress login credentials were saved in plaintext in the option fields mentioned above. (the smtp-credentials need to be saved somewhere, ok, but the wordpress credentials sould never show up in these fields!)
I couldn’t figure out why this happens. The input field for “SMTP Username” uses “dbem_smtp_username” as id and name – that should be sufficiently unique.
It happenened in Firefox 26.0 and Chromium 32, the latter one was used just once with the domain i tested this on.
Anyways, i worked around this with a quick hack in events-manager/em-functions.php line 621
Just add autocomplete="off"
to the input field.
What is the best way to fix this?