If every breaking change would lead to more income we'd be doing so well. What on Earth were they thinking, to change the default behavior for something that is in production use for so long. This was monumentally stupid, even if it is a windfall for the OP, it could have easily gone the other way. And props for figuring out what it was, likely there are some other people scratching their heads about this.
> After refunding everyone, we manually double checked the billing state of each account one by one and sent emails to apologize to each customer one by one; all 475 of them.
Yes, now imagine the other way around. How are you going to tell your users that you screwed up and will need to invoice them either again, or much closer to their next charge. Or maybe much later still if you don't spot the error right away.
Note that my comment isn't about the OP, but about the root cause of the breaking change: the driver.
Well, you described it as a "windfall for the OP" which really isn't accurate. Accidentally charging customers is a nightmare, and payment processors (rightfully) see large numbers of chargebacks as a red flag which can result in frozen funds / locked account. I'm not sure that the gem authors are benefitting from this either; it's open-source and they've probably lost users as a direct result of this article.
That they ended up returning it is good but either the amount was meant to have some kind of significance and before they returned it they received it.
I'm well aware of the effects of various kinds of risks to merchants.
