SplFileObject - Inconsistent behavior of seek and key with csv file

[Whip]

Description

In the code below, I'm opening a csv file, seeking to each line and trying to get the contents. $file->current() returns the correct line everytime but $file->key() returns 0 and then 1 for each line. This only happens when with READ_AHEAD and READ_CSV flags are used.

Note that o() is just a wrapper for echo and print_r.

The following code:

<?php
$file = new SplFileObject('import2.csv', 'r');
$file->setFlags(SplFileObject::READ_AHEAD | SplFileObject::READ_CSV | SplFileObject::SKIP_EMPTY | SplFileObject::DROP_NEW_LINE);
$file->seek(0);
o($file->key());
o($file->current());
$file->seek(1);
o($file->key());
o($file->current());
$file->seek(2);
o($file->key());
o($file->current());
$file->seek(3);
o($file->key());
o($file->current());

Resulted in this output:

0
id,status,on_sale,brand,name,link,meta_title,meta_desc,description
1
1,2,15,Samsung,M21,samsung-m21,Samsung M21,Samsung M21,Samsung M21
1
2,2,15,Samsung,M32,samsung-m32,Samsung M32,Samsung M32,Samsung M32
1
3,2,15,Samsung,M21,samsung-m21,Samsung M21,Samsung M21,Samsung M21

But I expected this output instead:

0
id,status,on_sale,brand,name,link,meta_title,meta_desc,description
1
1,2,15,Samsung,M21,samsung-m21,Samsung M21,Samsung M21,Samsung M21
2
2,2,15,Samsung,M32,samsung-m32,Samsung M32,Samsung M32,Samsung M32
3
3,2,15,Samsung,M21,samsung-m21,Samsung M21,Samsung M21,Samsung M21

If I remove READ_CSV flag, the line numbers I get are

0
2
3
4

Finally, If I remove READ_AHEAD as well, I get the expected output.

Looping through

When not using seek, everything works fine.

$file = new SplFileObject('import2.csv', 'r');
$file->setFlags(SplFileObject::READ_AHEAD | SplFileObject::READ_CSV | SplFileObject::SKIP_EMPTY | SplFileObject::DROP_NEW_LINE);
foreach ($file as $row) {
	o($file->key());
}

Outputs

0
1
2
3

I am attaching the csv file I used as well.

import2.csv

PHP Version

PHP 8.1.2

Operating System

Windows 11, Xampp 3.3.0