It probably worked just fine in perfect maintenance / test conditions, but degrades badly (very badly) when poor users, poor maintenance, and flying well past '

It probably worked just fine in perfect maintenance / test conditions, but degrades badly (very badly) when poor users, poor maintenance, and flying well past 'sane' response to errant sensors happens; as in this case. Testing new variations of software for a product that works when used as designed/tested already may have been (I'll speculate probably was, and at a low back-burner update priority baked in to some other larger change) in progress; but that's still re-testing and validating a complex system that must fulfill the other test cases (probably with real flight time and conditions). Particularly when a well trained operator (pilot) is supposed to be able to safely work around the existing defect, and seems to have done so in prior flights of that plain as well.