Payment Split: "Points Were Removed Because Order Total Has Changed"

I just bought a new laptop from Dell for college and received $38.95 in points from it. I wanted to use them and realized that I decided that I wanted to purchase a wireless mouse for it, which I find easier than the touchpad. I selected a $49.99 mouse and proceeded to checkout where I could apply my points and pay off the remaining $6.70 with my debit card. Eerily, once everything was applied, the order total still showed my student membership total of $44.99, which confused me, but I clicked submit order. It then rerouted me back to the review part of the checkout page and informed me that the points were removed from the order because the "order total had changed", which doesn't make sense to me, because why would the total change while processing the order? I checked around the internet and tried putting my debit card in first and THEN the points, but it still wouldn't register that I had applied any sort of Dell Credit. Can anyone help or am I not supposed to split between them like that?