An Undercover Tourist heads up, as this just happened yesterday:
If you sign up for the Mousesavers newsletter, they have a link to UT to get additional savings over their usual discount, some of the current discounts are quite good. ($14.50 additional savings on a 4-day with Extra day free (so 5-day) Disney Base ticket.)
I needed 4 tickets, but wanted to use 2 different credit cards to maximize some credits: Amex deal on UT right now gives a one time $30 credit, and I wanted to put some money on a Barclays card so I could use a travel credit later.
So, I bought 2 tickets with each card. Right after the 2nd transaction I realized the 2nd pair of tickets didn't have the expected additional discount. I got on UT chat and they tried to tell me that Mousesavers only allows a single discounted purchase (then told me a single purchase per month.)
Eventually they said they'd refer it to their billing department. Today I received a refund so ultimately got the full discount. UT stepped up and did the right thing, but was an unexpected annoyance.
UT says they'll email the e-ticket within 24 hours, but I actually got them within a few minutes. All linked to our account very easily.
So, the TL;DR: Moral of the story: sign up for Mousesavers newsletter, use their UT discount link, and either buy all your tickets at once or if you need to split things up like I did, perhaps use 2 different UT accounts to make your purchases.