It has been some time, but I want to add this for the record.
I agree with SImon that “Apple apparently simply didn’t test the update sufficiently.”
But I insist that there is no excuse whatever for not checking every change (every single change whatsoever; period) on every machine model. (No testing against only one T1 model. Test against every model.)
Testing is exercising software with the intent of breaking it.
If, after testing against many models, the software has not yet failed, testing is not finished. If you are a good tester, you are determined to do your very best to break the software. If there are any models on which your tests have not been run, you are not finished. Try those. Perhaps one of them will break the software. That is your goal.
Notice folks, that Google testers just the other day failed to test their software change on every computer model out there. You know what happened.
Credit to Google for owning up to their failure.