Surprise 2x exp

Ruby Coupon doesn't stack with event. You were receiving 2x exp from the event, not the coupon (under the assumption you had the coupon in your inventory in concurrence with the surprise exp event).

It does, actually. I usually don't care enough to train but I was bored enough to kill an hour so I decided to buy the 1 NX 1.5x coupon and it was stacking with 2x.