reporting on values calculated using formulas

I have a form that includes two user-entered number fields, RSVPs and Attendees. I also have a formula-based field that calculates No Shows as (RSVPs - Attendees). The problem is that I want to create a report that shows, for each site, the total number of RSVPs, Attendees, and No Shows, but Zoho is treating the No Shows field as a text field and thus will not allow me to sum the values. This makes no sense to me, since it's clearly calculated from two numeric fields and can only be a number. Is there a fix or workaround for this?