<?php
//IMPORTANT: Database-Name (here: tst) needs to have exactly 3 characters!
$dbLink=new mysqli("localhost","user","pass","tst",3306);

$dbLink->query("CREATE TABLE IF NOT EXISTS `sessionData` (
  `sessionId` varchar(60) collate utf8_unicode_ci NOT NULL,
  `pathHash` varchar(32) collate utf8_unicode_ci NOT NULL,
  `path` varchar(100) collate utf8_unicode_ci NOT NULL,
  `data` longtext collate utf8_unicode_ci NOT NULL,
  PRIMARY KEY  (`sessionId`,`pathHash`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci");
$dbLink->query("INSERT INTO `sessionData` (`sessionId`, `pathHash`, `path`, `data`) VALUES
('e75c7781166e3a361b7cff546563d5e8', '633fed500f479acaaaf54be8ec9ac657', '/bla', '0018a901234001222425678901235678345612341315789012345678901234567890123423456789012223456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678')");

$stmt=$dbLink->prepare("SELECT * FROM `sessionData` WHERE `sessionId`=?  AND `pathHash`=? LIMIT 1");
$arg1="e75c7781166e3a361b7cff546563d5e8";
$arg2="633fed500f479acaaaf54be8ec9ac657";
$stmt->bind_param("ss",$arg1,$arg2);
$stmt->execute();
$resData=$stmt->result_metadata();

while($field=mysqli_fetch_field($resData)){
 	$resFields[$field->name]=null;
}

call_user_func_array(array($stmt,'bind_result'),$resFields);
$result=array();		

while($stmt->fetch()){
	$tmpRes=array();
	foreach($resFields as $key=>$value){
		$tmpRes[$key]=$value;
	}
 	array_push($result,$tmpRes);
}

$stmt->close();
print_r($result);
?>

Above example causes crash also on my test server. (I removed other 
irrelevant comments)

Here is the shortest possible test I could come up with:

<?php

/* Test database and table with data:
drop database crashtest; create database crashtest; use crashtest;
create table crash ( test longtext );
insert into crash set test='123456789';
grant select on crashtest.* to 'test'@'localhost';
*/

$dbLink=new mysqli("localhost","test","","crashtest",3306);
$stmt=$dbLink->prepare("SELECT test FROM crash");
$stmt->execute();
$stmt->bind_result($foo);
while($stmt->fetch());
$stmt->close();
?>

The problem seems to be with the longtext column. If that is changed 
to text column, everything works just fine.

See also bug #46808

Yeah, you're right: Soon as I change the column-type from longtext to text, PHP doesn't crash anymore. The example you provided also crashes on my debug-enabled PHP-Version, while the Opensuse-Version (with Suoshin-Patch) throws efree()-errors until there are more than 396 characters in the textfield.
I actually tried to debug the PHP-code some (with very limited knowledge) and I think that the problem is somewhere within the binding of the resultset since thats where the script stops.

Here's better reproduce data (the longtext column has to have enough 
data to cause crash):

drop database crashtest; create database crashtest; use crashtest;
create table crash ( test longtext );
insert into crash set test='
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
';
grant select on crashtest.* to 'test'@'localhost';

In PHP_5_3 / HEAD the crash happens with any BLOB/TEXT types.
(due to mysqli_api.c:398)

This might be also a MySQL bug since it seems to set MYSQL_TYPE_BLOB 
always for any blob column.

Sorry, but your problem does not imply a bug in PHP itself.  For a
list of more appropriate places to ask for help using PHP, please
visit http://www.php.net/support.php as this bug system is not the
appropriate forum for asking support questions.  Due to the volume
of reports we can not explain in detail here why your report is not
a bug.  The support channels will be able to provide an explanation
for you.

Thank you for your interest in PHP.

This is indeed an issue with the MySQL cLient library. It works properly when using mysqlnd with 5.3 (--with-mysqli=mysqlnd) or when using MySQL's Connector/C, which is a standalone version of libmysql distributed witohut the server.

I didn't try using a current vcersion of libmysql bundled with the server.

I experienced this problem regardless of BLOB, LONGBLOB, TEXT, LONGTEXT etc...

However to fix, I found that if I called mysqli_stmt_store_result after executing the statement then the problem went away. The documentation says it increases performance but at a cost of memory, but I would argue that for BLOB's you should only be selecting them for a single row anyway.