tin's postinst writes to /etc/news/server without consulting the user
as long as shared/news/server is set.  Since the latter is a shared
variable, it is very likely to be set before tin is installed.

Overwriteing a configuration file silently is not something that should
be done by a package's postinst.

How do you propose to solve this?

I'd like it to not overwrite the file at all on my system.

Since there are probably others who do want it to be overwritten, I
can only propose that you add another debconf question about this.

Thanks,

I doubt I will do this, debian packages already ask way too many
questions. Let me know if you have different proposals.