Never used output buffering before but reading about it seems pretty straight forward. So this is what I did for testing:
<?php ob_start(); ?>
<p>Welcome to my homepage</p>
The problem is that the script is actually printing the paragraph onto my browser even though I have not flushed yet.
Is this not how output buffering should be used??
That's standard behavior. PHP will flush any open output buffers as part of script shutdown. That means you don't HAVE to call ob_flush() or the end/clean calls. It'll just happen automatically when execution of the script ends.
The only times you really do want to force a flush is if you're building up a "large" page and don't want it sucking up the script's memory limit, or you've gone past the point in your code where you'd need to do any pre-output operations, like header() calls.