How to add to an invoice all time tracked for a task?

When I am creating an invoice, I would like to be able to list all of the time (cumulative) tracked for each task on the invoice. I tried using the "Add to existing invoice" link on tasks -- but what I get on the invoice is "0 hours work at [amount] per hour" listed on the invoice -- even though the task is marked as "billable" and all the timetrackings are listed as "billable."

Is there a way for me easily to list all the tasks on an invoice -- with the cumulative hours calculated for each task -- so that I can easily get a cumulative total (all hours on all tasks for a project) on the invoice?