When using ob_start("ob_gzhandler"), be aware that the output buffer has to be flushed in order to invoke the ob_gzhandler callback function.
This may not always happen. For example, if you use ob_get_contents() to copy the output buffer to a string for further manipulation and then silently discard the buffer with ob_end_clean(), the output buffer is never "flushed" and as a result, the ob_gzhandler callback function is never invoked. And your pages won't be compressed.
This will be the case, for example, if you use the PHP Fusebox architecture/framework.
