Hi Riccardo,
I think the title of your post is misleading, which is probably one reason that people aren’t weighing in.
A bug is defined as something which behaves differently than it was designed to behave. I don’t think the fact that templates copy over members and collaborators is a bug; I think that’s the way the Asana folks designed it to work.
Now you might not like that design and would prefer that it behaved so it didn’t copy those elements, and that’s a totally valid request, which others have brought up as well (here’s one that I found). But to be clearer, you’re not reporting a bug but are making a request for a product change.
You might want to rename your post (or make a new one), something like “Provide option not to include members/collaborators in a template” or something like that; then people can vote on that.