default encoding

Hi there,
the default encoding in my database is “ISO-8859-1”. At least this entry is displayed in the properties of the database. But i am in doubt about it. Because-
when i insert an instance documnet with <?xml version="1.0" encoding="ISO-8859-1"?>, it will be changed automatic to <?xml version="1.0" encoding="utf-8"?>;
when i insert an instance without <?----?> part, <?xml version="1.0" encoding="utf-8"?> will be added to the document automaticly too.
I inserted the instances with x-plorer. Is there any setting to be changed?

Any suggestion is welcome.