PHP is working but post is displayed in raw html

I am entering this code into my post

[php]

header('Content-type: text/plain');
global $wpdb;

[/php]
<table>
	<thead>
		<tr>
			<th>&nbsp;</th>
			<th>Posts</th>
			<th>Avg. Length</th>
			<th>Total Length</th>
			<th>Comments (Mine)</th>
		</tr>
	</thead>
	<tbody>
[php]

for ($i = intval(date('Y')); $i >= 2002; $i--) {

	$from = $i;
	$to = $i + 1;

	$posts_count = $wpdb->get_var("
		SELECT COUNT(*)
		FROM <code>wp_posts</code>
		WHERE post_date >= '$from-01-01'
		AND post_date < '$to-01-01'
		AND post_status = 'publish';
	");
	$posts_length_avg = $wpdb->get_var("
		SELECT AVG(LENGTH(post_content))
		FROM <code>wp_posts</code>
		WHERE post_date >= '$from-01-01'
		AND post_date < '$to-01-01'
		AND post_status = 'publish';
	");
	$posts_length_total = $wpdb->get_var("
		SELECT SUM(LENGTH(post_content))
		FROM <code>wp_posts</code>
		WHERE post_date >= '$from-01-01'
		AND post_date < '$to-01-01'
		AND post_status = 'publish';
	");
	$comments_total = $wpdb->get_var("
		SELECT COUNT(*)
		FROM <code>wp_comments</code>
		WHERE comment_date >= '$from-01-01'
		AND comment_date < '$to-01-01'
		AND comment_approved = '1';
	");
	$comments_mine = $wpdb->get_var("
		SELECT COUNT(*)
		FROM <code>wp_comments</code>
		WHERE comment_date >= '$from-01-01'
		AND comment_date < '$to-01-01'
		AND comment_approved = '1'
		AND user_ID = 1;
	");

[/php]
		<tr>
			<td>[php] echo $i; [/php]</td>
			<td>[php] echo number_format($posts_count, 0); [/php]</td>
			<td>[php] echo number_format($posts_length_avg, 0); [/php]</td>
			<td>[php] echo number_format($posts_length_total, 0); [/php]</td>
			<td>[php] echo number_format($comments_total, 0); [/php] ([php] echo number_format($comments_mine, 0); [/php])</td>
		</tr>
[php]
}
[/php]
	</tbody>
</table>

And the code is giving the desired results. However, when I preview the post the raw html (source code)is displayed instead of my website. What is going wrong?

http://wordpress.org/extend/plugins/allow-php-in-posts-and-pages/