The change of php 5.2 to 5.6 modifies the characteristics of the opening and closing script

Question

The opening of the scripts change

The closure of the scripts changes ?> to ...--?>

The scripts are not executed

I searched the web possible causes, but I have not found anything.

Please, I ask help

Example:

<?php
    session_start();
    $codigo_isef =  md5(uniqid(rand(), true));
    $codigo_isef  = trim($codigo_isef); 
?>

to

... <!--?
    session_start();
    $codigo_isef =  md5(uniqid(rand(), true));
    $codigo_isef  = trim($codigo_isef); 
...--?>

Let me explain:

I open with ""

The browser does not process the code and change the characters "...