I was having a lot of problems with getting my cart to work

I was having a lot of problems with getting my cart to work (it wouldn't work on the SSL, and then it wouldn't complete an order even on non-ssl), and I found this thread:

https://premium.wpmudev.org/forums/topic/whmcs-checkout-not-completing-transaction-when-complete-order-is-clicked

Changing away from the comparison cart solved all of the problems I was having. Is this a known problem? Or is there something else at work here that needs to be corrected?