Fixed the pmpro_paypal_express_return_url_parameters filter to properly encode the & and = so it gets added to the ReturnURL param instead of being interpretted as its own param.
Fixed pmpro_paypal_express_return_url_parameters filter to properly encode & and = so the params are properly added to the ReturnURL instead of being seen as extra params to the full PayPal Express URL. The PMPro Addon Packages plugin has been updated to take advantage of this to make that plugin more compatible with PayPal Express.