PHP PDO is saving string from javascript object (ajax) as empty field - php

Question

This is interesting and by that I mean incredibly frustrating.
I am passing this data to my php file via an ajax call: {"html":"<div>I'm a div!!</div>"}
I want to preface this next statement by saying that I do understand the reasons for not saving json to a database, but it does have a use here.
When I save this data to the database field, the field is empty. Now see this:
$in1 = file_get_contents('php://input'); //from ajax
var_dump($in1);
$in2 = '{"html":"<div>I\'m a div!!</div>"}';
var_dump($in2);
value of my ajax call:
string(33) "{"html":"<div>I'm a div!!</div>"}"
string(33) "{"html":"<div>I'm a div!!</div>"}"
Perfectly the same! Yet, $in2 will save to the database just fine!! While $in1 yields an empty field!!
To be certain, consider this:
if ($in1 === $in2) { echo "They're equal!"; }
Go figure...they're exactly equal, yet one will save correctly and the other won't. Amazing.
Further: mysqli does not have this issue, so that narrows it down to being a PDO issue.
$query = "UPDATE plugin_instances SET config=(?) WHERE id=2";
$stmt = $mysqli->prepare($query);
$stmt->bind_param("s", $in1);
$stmt->execute(); //correct value in the db!!
I have now removed everything and this is the whole php file.
Non-working output
Working output
The only difference between these two is the result of $stmt->rowCount().
The sample that correctly updates the field says int(0) and the one that empties it says int(1).
$db = new PDO('mysql:host=localhost;dbname=disarray', 'root', 'temp');
$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
var_dump($db);
$params = [':foo'=>'{"html":"<div>I\'m a div!!</div>"}'];
var_dump($params);
$params = [':foo'=>file_get_contents('php://input')];
var_dump($params);
$query = "UPDATE plugin_instances SET config=:foo WHERE id=2";
var_dump($query);
try {
$stmt = $db->prepare($query);
var_dump($stmt);
$stmt->execute($params);
var_dump($stmt);
var_dump($stmt->rowCount());
}
catch (PDOException $e) {
echo $e->getMessage();
}

Answer 1

Massive sigh. The issue is with my javascript, not php. I was testing this out in my api, which several things make calls to throughout my somewhat large app. There was an additional ajax call being made that I was unaware of (it was left in the code by error) and it wasn't sending any data, so my test script in the api was running with no data and thus emptying the database field right after I wrote to it. Of course, entering the data directly into the script worked out great because both calls were doing the same thing.
It is unfortunate that when I stripped down my php code, I used the same filename/location.
More unfortunate is that the success of the mysqli threw me even further off, solidifying in my mind that the issue was with PDO. It turns out that it was just changing which ajax call was responded to last.
And thus, I have hopefully learned not to have so much tunnel-vision when going through the debugging process.