Threes!

My wife and I just downloaded and are playing Threes!. Its a great game and we are really enjoying it. I noticed, however that our individual scores are showing up on each others devices even though we have different Game Center logins. I even signed out of both of our Game Centers on our individual devices and our scores are still being synced and combined.
I am not familiar with how the game saves data, but is this normal? We share the same iTunes Apple ID, but different Game Center IDs.
Anyone else run into this problem or is it normal?

Thanks in advance.

I was thinking since my wife and I have different Game Centers Apple IDs that the game would save the individual scores separately. We do use the same iCloud backup for our devices though.