Except in this case the explanation came a few weeks later. But it did come, just as my colleague predicted.
My taxes are incredibly simple and straightforward but this year there was one slight oddity having to do with moving a 401K account from one company to another. This yielded a bit of extra tax for me (don't ask) and the amount of the refund was in the general neighborhood of what I determined I owed on that money, so I figured I had just been wrong about owing tax. So I cashed the check and felt a little bit richer.
Ah, but then I got the explanation in the mail. The reason for my refund, according to their records, is that the IRS decided that I'm entitled to a higher standard deduction than I claimed because I or my spouse is over 65 and/or blind. Ok, not all of you actually know me personally, but really I am neither over 65 nor legally blind and my filing status is single.
So I called the number on the statement. It was a long wait to reach somebody, but the IRS representative was very pleasant. I was sure to begin my conversation right up front with one simple statement saying what my issue was, making it clear that I felt I had received money in error and wanted (a) to verify this and (b) to pay it back immediately. Yes, she agreed there seemed to have been an error. She checked on my file and made some vague comment about this coming from "The Fresno office". She said that she was putting a note in my file that I'd be contacting the Fresno office, but she wasn't going to correct the file herself or else I would get a bill of some sort for the money from the IRS. She said that when the Fresno office receives my note and check (and she told me where to send it and what it needed to include) they should correct my account then and there and send me a notice that it had been corrected. And so I did. And now I hope that this is the end of it.
Once I saw that this was likely an odd and unlikely error I knew I'd send the money back. It just isn't my money. I said as much to the IRS representative, and she said while she couldn't guarantee that this would be so, it was in fact unlikely that they'd later see their mistake on their own. She said that even if they did I wouldn't have to pay any penalties or interest because it was their mistake. Maybe she only told me this because by that point it was too late for me to change my mind, but I wouldn't have changed my mind anyway.
I've told a few people that I honestly believe that this sort of thing comes back to you in the long run -- keeping money that comes to you in error -- and they seem to think I mean that I will be found out and this will cause trouble. But no, that's not what I mean. It just doesn't work out in the long run in terms of living your life peacefully if you don't return the money.
There's a tiny part of me that feels I'm entitled to a small bit of resentment that because of the IRS's error I had to go through the bother of trying to fix this. But really, this didn't take long and nothing was terribly frustrating or cumbersome. And for a brief few weeks I felt about $300 wealthier than I really am, and that was sweet.