You have to enable auto return in your PayPal account, otherwise it will ignore the
From the documentation (updated to reflect new layout):
Auto Return is turned off by default. To turn on Auto Return:
- Log in to your PayPal account at https://www.paypal.com. The My Account Overview page appears.
- Click the Profile subtab. The Profile Summary page appears.
- Click the My Selling Tools link in the left column.
- Under the Selling Online section, click the Update link in the row for Website Preferences. The Website Payment Preferences page appears
- Under Auto Return for Website Payments, click the On radio button to enable Auto Return.
- In the Return URL field, enter the URL to which you want your payers redirected after they complete their payments. NOTE: PayPal checks the Return URL that you enter. If the URL is not properly formatted or cannot be validated, PayPal will not activate Auto Return.
- Scroll to the bottom of the page, and click the Save button.