PHP8.2 ignores local value of `output_buffering` and uses master

I want to set output_buffering=0 in a single directory. When I create a .user.ini file in that directory with output_buffering=0 , phpinfo() shows 0 for the the local value, and 4096 for the master, but the actual behavior PHP exhibits is as if output_buffering=4096.

In other words, PHP appears to be ignoring the local value and instead using the master value.

Apache is configured to use PHP-FPM with SetHandler, not ProxyPass:

<FilesMatch \.(php|phar)$>
    SetHandler "proxy:unix:/run/php-fpm/www.sock|fcgi://localhost"
</FilesMatch>

This response should arrive in three chunks, one second apart each - with or without the str_repeat(…) call. In actuality it only does so when str_repeat(…) is uncommented. When I set the master value of output_buffering=0 I get the behavior I want without str_repeat(…), but not when I set the local value.

header('Content-Type: text/text');
for ($i = 0; $i < 3; ++$i) {
  echo $i;
  // echo str_repeat(' ', 4094);
  echo "\n";
  flush();
  sleep(1);
}

According to the PHP documentation for output_buffering output_buffering is modifiable per directory.

Interestingly, despite the setting in .user.ini affecting the displayed local value, phpinfo(), does not show .user.ini in "additional .ini files parsed"