Fabian, First, sorry for the delay replying. Gmail though it was spam (unfortunately it happens more than it should, specially with bug tracking systems), and I only noticed the bug it now.
Thanks for your detailed bug report. Definitely silently overwriting config files is a bug. About the current /etc/mailname usage, it was my interpretation of the debian policy, but according to your example, it's not coherent. I'll read carefully to the policy once more, and check what is being done on other similar packages. Cheers, José Fonseca