editing files with nano adds a bytemark to the file which nginx prints to the client

When we have to edit php files on the webserver, sometimes our website prints out part of what i think is a bytemark to "lock" the file from nano. On the website, it then adds weird strings like for example:

b0nano 4.8��roothostnamefilename.class.req.php

where hostname is the name of the ubuntu server and the rest is the filename of the php file. That obviously shouldnt happen and i'm afraid that it exposes information or makes files editable by guessing their location and url.

Is there a way to keep nano from doing that or avoiding printing out that string? One time it caused an index.php script to just print out its contents to everyone instead of being executed.