Problem using PHP internal zlib compression

I'm using apache 1.3.31 with php 4.3.7. The previous system was apache 1.3.28 + php 4.3.3, and had the same problem. Apache is serving both http and SSL pages. mod_zip is activated for http hosts and disabled for SSL hosts. To correct the inability of mod_gzip and mod_ssl to inter-operate I've enable php compression on the SSL site. Note: for the test I'm using a standard http test host with mod_gzip disabled My problem is this : php_value zlib.output_compression On produces compressed php pages, but without the "Content-Encoding: gzip" header. The consequence is that browsers are not decompressing the pages. php_value output_handler ob_gzhandler Works correctly. I've access to the server of a friend. He is running apache 1.3.29 php 4.3.4 on a debian server (all binaries from debian) and doesn't have this problem. I've compared our config files and nothing special appears. What could be the source of the problem ? A configuration error in apache and/or php ? Since this system is compiled by me, am I missing a php module ? -- Marc