This solution does not work for me.  Every time I convert an estimate into an invoice it reverts to the old invoice template.  I then have to select: Formatting --> Manage Templates --> and select the new template.

The next time I convert an estimate to an invoice I have to go through this process all over again.

There has to be a way to set the newly created invoice as a default.  In this day an age something like this shouldn't be so complicated.