Thank you for using our services and bringing this up to our attention. Actually, here's how templates and issues work. If at the beginning when you created a campaign it was based on a template, the first issue will use this template. However, the second issue will be based on the last issue that was sent, and this is done on purpose, because when you use a template, you can modify it to a state, where it doesn't look like the template anymore. However, you will still want to have the same or similar appearance for the issue that will come after this issue. This is why each issue is based on the last issue, that was sent, not the template itself and changing the template will not affect it.
Hope you find this information useful. We'll make sure to make this more visible in the documentation.