After you authenticate, you put your phone near the reader and it told you multiple card detected? This happen often? Probably something wrong with the phone. If not, if only met once, it could be the reader. If you authenticate one card, it will only let you pay with that card. If you don't put a transport card, you won't be able to tap mrt/bus without authentication. It's only after you add that one card as transport card den you can use that one card for transport (without authentication). I believe it's the same for all if not most ppl here. I've never heard of ppl having the same issue as you.
