We filed our taxes electronically back in March and received our refund shortly afterwards. Everything was fine.
Then we received a check in the mail from the IRS for a refund. No explanation. No forms. Nothing. Just a check made out to us at our new address. Since it was at our new address we knew it had to be from this year. We also knew we were not entitled to any additional refund.
Always never trust the IRS.
After spending over an hour on the phone trying to find a live person instead of a recording, we finally received the answer.
Apparently, somehow the IRS matched someone else's return to ours, looked at the filing and decided we needed a refund of the difference. Yeah, not sure how that happened.
If we had not checked into it and would've cashed that check, I'm sure some months, or years, down the road the IRS would've discovered its own mistake (possibly) and then expected us to not only return the original amount but probably would've fined us and charged us interest, because that's how it works.
Moral of the story: Keep records. Know your return. Never blindly cash a check from the IRS. And, most importantly, always never trust the IRS.