"Sometimes the refund amounts don't recalculate at all when choosing "Prior Year option" and there is a $10,000 difference in Earned Income."

Might this be correct? Depending on what else is on the return, it could be. And refund amount is not the the correct comparison. Refunds =  total payments and credits - total tax. If payments are low or nonexistent (unemployment anyone?) there won't be a refund.

Have you done the calculations manually to check?