It's hard to see what you're saying as your question is formatted so badly that the whitespace that you are talking about disappears. Please use <code> tags round your code examples.

Your problem is that the blank line you are introducing is taken as ending the CGI headers. Therefore your header is seens as being part of the body of the response and the web server adds its own default content-type header (probably saying that the content is text/html). You can't have that blank line there as the first blank line in the response defines the end of the header.

Update: Now that Corion has added code tags I can see what you're doing a little more clearly. I'm not sure why it's working as it is, as you need you insert a blank line between the end of the headers and the start of the content.