Membership Receipt shows wrong contribution

Steps to reproduce

1) create offline membership & receipt payment
2) renew & receipt another payment
3) choose 'edit' and send out a receipt

The receipt that goes out has the details of the earliest contribution not the latest contribution.

The smarty value {$formvalues.total_amount} is set to this contribution

I fixed this for the customer by changing the template (workflow templates / offline membership receipt) to use

{$rows[0].total_amount} instead

It works but I'm not sure if it is the 'right' solution