Not receing all posted data from PDF form to php

I am sending data from a PDF form with a submit button in HTML format to a php script for further processing. The form has many fields arranged in rows like this:

a group of radio buttons named: row[i][answer], then inline some text fields named: row[i][ov], row[i][plo], row[i][plcv], row[i][pls], row[i][plx] (where i is incremented from 0 to 100)

On submit i post all this data to a php script like this:

$row = $_POST['row']; 

Now the problem is that for some reason i receive all data but row[i][answer] and row[i][plx]…those 2 fields are being copmletly ignored and i cannot find a reason for this.

I did <pre><?php print_r($row); ?></pre> and there it is all the data but those 2 fields:

Array
(
    [0] => Array
        (
            [ov] => Some text.
            [plcv] => N/A
            [plo] => Art. 4 
            [pls] => N/A
        )

    [1] => Array
        (
            [ov] => Some text.
            [plcv] => N/A
            [plo] => Art. 10 
            [pls] => N/A
        )
    . . . 

There should be also [answer] and [plx] but they are compleetly missing.

I also did it with file_get_contents("php://input"); and same result, [answer] and [plx] are missing.
Any ideas why this happens?