WordPress Shortcodes not working with couponpress

I am using WordPress 3.3.1 and a theme couponpress. I am trying to display current month and year in the posts. Below is the code i am using (added in theme’s functions.php).

function displaymonth(){
return date('F');
}
add_shortcode('month', 'displaymonth');

function displayyear(){
return date('Y');
}
add_shortcode('year', 'displayyear');

Then i go to edit post and replace month and year with [month] [year]. Instead of showing the current month and year, it is showing up the code i.e. [month] [year].

Am i missing something here? Please help.

Thanks in advance.