Mystery Ward

Hi there not sure if this is a bug or not but I was buying the blue essence shop Mystery Ward Pack and it told me I "unlocked" the same ward on two pairs of wards and it was back to back. The chances of receiving the same ward out of how many wards there are is pretty slim isn't it? Yet it happened to me twice in a row. Also if I already "unlocked" a ward, how can it be unlocked again? I already got it so it shouldn't even be available to be unlocked again. I'll just avoid getting it until I know for sure since it's just a waste of essence to get multiple of the same ward back to back.