Comment 11 for bug 1509083

Based on the examples here and the referred Apache bug I recreated this and confirms that it works.
There were some proxy fixes recently, maybe one of them affected this as well without knowing about it.

Steps to reproduce:
trusty container
apt-get install php5-fpm apache2 libapache2-mod-fcgid

config for the site is:
cat /etc/apache2/sites-available/test-fcgi-proxy-pass.conf
  DocumentRoot /var/www/html
  ProxyTimeout 600

  <Directory "/var/www/html/">
   Options -Indexes
   Require all granted
   AllowOverride All

  <LocationMatch "^/(.*\.php(/.*)?)$">
    ProxyPass fcgi://$1

enable site and enable proxy
   ln -s /etc/apache2/sites-available/test-fcgi-proxy-pass.conf /etc/apache2/sites-enabled/
   ln -s /etc/apache2/mods-available/proxy* /etc/apache2/mods-enabled/
   ln -s /etc/apache2/mods-available/xml2enc.load /etc/apache2/mods-enabled/
   ln -s /etc/apache2/mods-available/slotmem_shm.load /etc/apache2/mods-enabled/

Change the default local socket to match apache config in /etc/php5/fpm/pool.d/www.conf
listen = 9000

Now place a long duration script as /var/www/html/foo.php
    error_log("executing script... ");
    $time = time();
    for ($t = 0; $t <= 290; $t+=5) {
        error_log("Logging: $t (".(time()-$time)." seconds)");
        print("Logging: $t (".(time()-$time)." seconds)");
    error_log("execution done (".(time()-$time)." seconds)");

then access your servers apache to the php file, gets redirected and takes a while

It would now be up to the initial reporter to check if it works for them as well.
Setting to incomplete until we hear again.