For Contribution Profile, cancelled transaction prevents future transactions (PayPal Std)

using paypal std, if a user (logged on or not) fails to complete a transaction after departing to paypal, an attempt to create a new contribution using the same information will not be routed to paypal.com. the "continue" button will go to "processing", and then user will be returned to original profile page.

this is a particularly serious problem considering how confusing paypal is (especially for recurring payments).

(not tested on sandbox; is there a way to do so?)