I'm having a lot of difficulty with it too. It keeps adding things to my cart, and when I delete them it empties the stuff I actually wanted to buy. It also auto filled in someone else's email on the login page. Scary.
Yep, it appears they have a bug with sharing accounts / carts / sessions. Highly recommend you don't try to check out on this site for the time being as you may accidentally be charged more/less than you expect to.
I had some funny stuff happening with my cart the first day of the sale but I waited a bit and finally placed an order with no issues just now before the sale ends. Took me a bit of time to figure out what I wanted and then the Exceed bundle became back ordered (I am not sure that I would have gotten it anyway since I already have one of the sets, I'll probably just pick the rest up here and there), but I finally nailed it down. Shipping was $9.XX for two day priority, which wasn't bad I guess. I got the Pixel Tactics playmat (been wanting it for a while), two of the Exceed promo characters (Juno and Skull Man), and Dragon Punch for $45 shipped.