If you have zlib.output_compression set to on when your script starts (in php.ini or via apache directive), then you disable it at runtime using ini_set() before producing output, your output will still be buffered! Even if you call ob_implicit_flush().
If you want unbuffered output, you must disable zlib.output_compression before your script starts (as well as mod_gzip of course, if you have both installed).
This behaviour experienced on Server: Apache/1.3.33 (Debian GNU/Linux) mod_gzip/1.3.26.1a PHP/4.3.10-18
