Page with custom URL parameter redirects

I have a page template that produces different results based on a ?year=x parameter on the end of the URL, eg wordpress.com/page/?year=2011

This works fine for some ‘year’ values but for others it doesn’t load the page and instead redirects to a random posts (which is from the year specified and has the page slug in its title).

Is the ‘year’ parameter reserved by WordPress?

To try and make it work I added this code to my functions.php

function minisite_query_vars($vars)
{
    $vars[] = 'year';
    return $vars;
}
add_filter('query_vars', 'minisite_query_vars');

… and am accessing it using get_query_var(‘year’) but it still does not work as I would like.

Any ideas on how to get this working? Thanks in advance.