The widget for the Knews mailing list subscribe form has the ID "email" for the email form field. The email field in the standard WordPress comment form uses the same ID "email".
This means that any pages that show the widget, as well as the comment form do not validate as proper HTML, because you can't have duplicate IDs for HTML elements.
This can also cause problems with scripting and style referring to #email, as unless you specify the context further, rules will apply to both fields. Though this is possible, it is still not correct to have two ID's that are the same on a page, and it may cause problems upon activating the plugin if you already refer to the #email in the WordPress comment form.
Using something like #knews-email instead of the generic #email in your signup widget would avoid this conflict, as I can't find any way to change the ID on the WordPress comment form.