Possible bug: update_user_meta is updating two unique meta entries

On a CPT page I am checking to see if the user is logged in; if they are, I’m checking to see if they have a meta entry which is 'session-' + the current page’s stub. If they do, I increment the value by one.

I thought this was all working fine, but I’ve just noticed that it’s actually incrementing two separate user_meta fields. At the moment I have three CPT pages (let’s call them Burt, Ernie & Ralph); if I refresh the page for Burt, it increments my user_meta field (session-burt) by 1, which is great; however it also increments session-ralph by 1.

I don’t have the Ralph page open, and I’m echoing out everything I can think of to try and trace down the erroneous line of code, but I can’t see why it’s doing it. It is incredibly annoying.

Here’s my code. Hopefully I’m just blind to something really obvious and it’s not a WP bug.

$stub = $post->post_name;

$sessionKey = 'session-' . $stub;
$viewedKey = $stub . '-lastviewed';

$sessionViewsArray = get_user_meta($current_user->ID, $sessionKey);
$sessionViews = (int)$sessionViewsArray[0];

echo '<pre>';
print_r($sessionViewsArray);
echo '</pre>';

echo '<h1>I think there are ' . $sessionViews . ' views</h1>';

$lastViewedArray = get_user_meta($current_user->ID, $viewedKey);
$lastViewedTime = $lastViewedArray[0];

if ($lastViewedTime) {
    $lastViewed = date('l jS F Y, g:ia', $lastViewedTime);
} else {
    $lastViewed = 'First time - good luck!';
}

$newSessionViews = $sessionViews + 1;

update_user_meta($current_user->ID, $sessionKey, $newSessionViews);
update_user_meta($current_user->ID, $viewedKey, time());

echo '<h1>I think I just updated ' . $sessionKey . '</h1>';

///
//  Now let's update the page views
///

$pageViewsArray = get_post_meta($post->ID, 'totalviews');
$pageViews = (int)$pageViewsArray[0];

$pageViews += 1;

update_post_meta($post->ID, 'totalviews', $pageViews);

It’s worth noting that it only seems to be the one session-ralph entry that is affected; the ralph-lastviewed entry doesn’t get updated if I refresh the Burt page.

Any help would be greatly appreciated!

UPDATE:

As per the awesome answer from @dalbaeb below, my solution was to use the following hook:

remove_action('wp_head', 'adjacent_posts_rel_link_wp_head', 10, 0);

…which removed the <link rel='next'... and <link rel='prev'... tags from my header and immediately solved the issue.