Description:
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Apache is crashing systematically with error:
AH00428: Parent: child process 9628 exited with status 255 -- Restarting.

APACHE error log:

[Tue Jul 14 15:02:13.038276 2015] [mpm_winnt:notice] [pid 7044:tid 404] AH00428: Parent: child process 9448 exited with status 255 -- Restarting.
[Tue Jul 14 15:02:13.324305 2015] [mpm_winnt:notice] [pid 7044:tid 404] AH00455: Apache/2.4.9 (Win32) PHP/5.5.12 configured -- resuming normal operations
[Tue Jul 14 15:02:13.329306 2015] [mpm_winnt:notice] [pid 7044:tid 404] AH00456: Apache Lounge VC11 Server built: Mar 16 2014 12:13:13
[Tue Jul 14 15:02:13.329306 2015] [core:notice] [pid 7044:tid 404] AH00094: Command line: 'C:\\Program Files\\wamp\\bin\\apache\\apache2.4.9\\bin\\httpd.exe -d C:/Program Files/wamp/bin/apache/apache2.4.9'
[Tue Jul 14 15:02:13.352308 2015] [mpm_winnt:notice] [pid 7044:tid 404] AH00418: Parent: Created child process 3140
[Tue Jul 14 15:02:14.528388 2015] [mpm_winnt:notice] [pid 3140:tid 332] AH00354: Child: Starting 64 worker threads.

I checked windows event and I found httpd.exe is crashing caused by php5ts.dll

Test script:
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HOW TO REPRODUCE:

PHP code:

$mysqli=new mysqli(DB_HOST, DB_USERNAME, DB_PASSWORD, DB_NAME);

if (!($stmt = $mysqli->prepare("CALL test()"))) {
    echo "Prepare failed: (" . $mysqli->errno . ") " . $mysqli->error;
}

if (!$stmt->execute()) {
    echo "Execute failed: (" . $stmt->errno . ") " . $stmt->error;
}

do {
    if ($res = $stmt->get_result()) { //Apache crash on this call
        printf("---\n");
        var_dump($res->fetch_assoc());
        mysqli_free_result($res);
    } else {
        if ($stmt->errno) {
            echo "Store failed: (" . $stmt->errno . ") " . $stmt->error;
        }
    }
} while ($stmt->more_results() && $stmt->next_result());

Store procedure code:

CREATE DEFINER=`root`@`localhost` PROCEDURE `test`()
BEGIN
declare test_var varchar(100) default "ciao";
declare bNoMoreRows bool default false;
declare test_cursor cursor for
    select id from tmp_folder;
declare continue handler for not found set bNoMoreRows := true;
create temporary table tmp_folder select "test" as id;
open test_cursor;
fetch test_cursor into test_var;
close test_cursor;
select test_var;
drop temporary table if exists tmp_folder;
END

Expected result:
----------------
I expect to read "test" in the browser

Actual result:
--------------
Apache is crashing