I agree completely. I'm tempted to call it a clear falsification of any "reasoning" claim that some of these models have in their name.

But I think it's possible that there is an early cost optimisation step that prevents a short and seemingly simple question even getting passed through to the system's reasoning machinery.

However, I haven't read anything on current model architectures suggesting that their so called "reasoning" is anything other than more elaborate pattern matching. So these errors would still happen but perhaps not quite as egregiously.