There's now an idea that that robustness principle was backwards. The classic example being web browsers which were so liberal they encouraged all sorts of weir

There's now an idea that that robustness principle was backwards. The classic example being web browsers which were so liberal they encouraged all sorts of weird non-standard web pages which now have to be supported forever. If a PNG app trusts the spec, and the library doesn't comply, and that causes the app to crash. That's a good thing overall. It would lead to somebody discovering the problem and hopefully fixing it. It's only a bad thing for the specific app that crashes. Or in this case, risks getting exploited. Maybe for security, the principle doesn't apply the same way.