Weird failure in PHP if statement

OK, so here's my code. (I'll sanitize it later. Don't worry about it.)

<?php
include_once('../basics.php'); //Site configs
include_once('class.user.php'); //For storing user data and stuff
include_once('class.image.php');
include_once('auth.php'); // The user authenticator

// Check if user wants to upload to existing or new album
if (isset($_POST['album'])) {
    if ($_POST['album'] == '') {
        $_POST['album'] = $_POST['new_album'];
    }
}

// Populate album dropdown menu
$albums = $database->query("SELECT DISTINCT(album) FROM images")->fetchAll(PDO::FETCH_COLUMN); 

// Load the 'upload new photo' interface if user's not uploading it already
if (!isset($_FILES['image_link']) || !isset($_POST['caption']) || $_POST['caption'] == '') {
    //var_dump($_FILES);
    //var_dump($_POST);
    include('views/gallery_upload_new.php');

// Otherwise store the image file, register it into database, and put the user back in the list of photos
} else {
    $new_image = new Image($_POST['caption'], $_POST['album']);
    $new_image->register($_FILES['image_link']['tmp_name'], $_FILES['image_link']['name']);
    header('location: gallery_management.php'); 
}
?>

Here's the weird part: without those two var_dump's up there, the else block won't execute. I've made sure the indexes in the $_POST and $_FILES are correct. Yet without those dummy dumps, this thing won't work. It doesn't even matter if they're commented out or not. They just need to be there.

What did I do wrong? Did I made a syntax error somewhere?