Working with id attribute breaks on some pages

I saw that text within input field is select via "#edit-mail". This is wrong, since when a comment form is loaded or in user register page, ID of simple suscription is "#edit-mail--2", because there is already an mail input type.

i changed this "#simple-subscription-form #edit-mail" to "#simple-subscription-form>div>div>input", to select input via html structure and not ID.

Hope it helps someone.