Thank you to the colleague/customer/product owner, who found the bug I missed. That oversight, was (at least in part) my mistake. I've been thinking about what happened and what that means to me and my team.
1) Opened my eyes to a situation I'd never have thought to investigate.
2) Gave me another item for my checklist of things to check in future.
3) Made me remember, that we are never done testing.
4) Are never sure if the application 'works' well enough.
5) Reminded me to explore more and build less.
6) To request that we may wish to assign more time to finding these issues.
7) Let me experience the hindsight bias, so that the edge-case now seems obvious!