Unfortunately, the software that handles the upgrade licenses uses the original purchase/renewal date the calculate expiration dates. Upgrades do not change that date.
I do agree with you that the upgrade date should be the new expiration date. But I see how it makes sense both ways. That said, when I see updates purchase, I do adjust the renewal data accordingly. So, you’ll see that the expiration date is now 5/5/2017.
Apologies for the confusion and thank for you purchases!