How does IntelliJ modify Charset.defaultCharset?

Execute this in IntelliJ:

public class Main {

    public static void main (String[] args) {
        System.out.println(Charset.defaultCharset());
    }
}

And it will most likely print "UTF-8". Now export it as runnable JAR file and execute it with the same Java binary - and (under Windows) it will print "windows-1252".

Then, explain to me why this happens :-) Please?