It's called closing the loophole. Their original intentions was probably for existing customers to pull in new Starbucks cards adopters, not for existing ones to manipulate it. How would you feel if some customer managed to horde 100 or 200 drinks to him/herself? Not fair right?

Probably should've sent the free drink to a card registered under a different name. That was probably the only and "legit" way.

I assume the anniversary tumblers are originally priced at RM48, but with RM15 discount it goes down to RM33.

I got the hibiscus one for my mom few months ago and planning to get the wau one. Free drink too!

Yes. To clarify further with an example, let's say I'm a new customer and I get a new Starbucks card with RM50 credit.

Once I register the card online, I automatically get a free drink. Next I use it to purchase a RM33 Wau tumbler, I get a second drink for free.

So in total, you'll end with 2 free drinks (normally costs RM20-30), a nice tumbler and RM17 of credit in your card remaining, enough to buy one more drink. Remember to use your tumbler to get a further RM2 discount.

Free drink after card registration is only valid for only once I think. If you get a 2nd Starbucks card under your own name, no free drink after registration.