Comment 9 for bug 1407990

The root cause of the problem has been determined to lie with the apache2handler for PHP. It is not sufficiently up to date to function well with Apache 2.4 receiving pipelined requests. A patch for the most common setup has been developed, but it has not yet been integrated upstream.

I have also put in an enhancement request at https://bz.apache.org/bugzilla/show_bug.cgi?id=57756, for a configuration option that could provide a fallback for server administrator, because this may equally affect other Apache 2.4 add-on handlers that have not undergone rigorous testing for this use case.