email template with invalid (underlying) url?

Hello - I have an email template that includes a url. The querystring parameter value is set to a column in the database. When the email is sent, the url is rendered correctly in the email.  However, the underlying value of the querystring parameter is different. This seems like an odd error.  I'm not even sure how a different underlying qs param could be getting set?  Any idea what might be causing this behavior or how to debug?