Do you or your team review every item of every changelog of every dependency in your stack (recursively for their dependencies) for every minor update, and/or 100% coverage for all of your assumptions of how they are used?

Sure it was a mistake by OP in TFA but it's an honest mistake any of us could make. And it's a really Bad Move by the Mongoid devs. It'd be a bad move in 1.2->1.3, but by 7.3? I'd just be like "whelp, this is how this function behaves now in perpetuity, I guess just document that it has different semantics than AR" even if an 8.0 was released. This is the kind of change which causes really subtle bugs. It's rarely worth it. Just introduce .chain_or() or something.