When I change one of my custom template files, and then want to save it, I get a warning that it's created with an older NWCfile format and the original version will no longer be able to open it.
This seems normal, so I click 'yes' to proceed.
But after that, the template file is disappeared. It's not showing in the template/custum folder, nor in the folder where I keep my NWC songs.
It might be of use to look at:
"Song Templates in 2.51"