Issues using Paypal and the PayPal Plugin Mastercard Number?

So yesterday I placed an order at a reputable company for a new toy – they didn’t take Amex which was a complete letdown – but then again, the processing fees are higher with them so I can understand.
So I went off to use my Paypal account – since they took Mastercard, I used the Paypal Plugin to auto generate a mastercard # so I could buy my toy. Turns out, while this store accepts Mastercard, they don’t accept the Paypal auto generated Mastercard # – what a major pain.
Anyone else seen an issue like this where a store wouldn’t accept a Paypal Mastercard #?
