PayPal cancel recurring payments

When a user buy a level (not upgrade) Paypal: 1) create a recurring payments 2) cancel the recurring payments 3) send a payment 4) Site license is ok.
When a user buy an upgrade: create a normal recurring payment and upgrade normally site license.

Is that normal? Why PayPal Cancel the subscription? Why when a user buy un upgrade don't pay?

Best Regardes,

Guido Tocco