The problem isn't so much "typical programming errors", but the appoach to solving problems. So, it's not that there are tons of buffer overflows in the code (well, not that I know of, though I didn't explicitly look for them either), but stuff such as the vulnerabilities in the DNS resolver because they reimplemented things from scratch without the necessary domain knowledge on how to do that securely that has been collected and implemented by the dozens of existing implementations over the decades, or the bug that caused .* to match .. and thus systems to be destroyed by the temp cleanup code, which is equally a potential pitfall that is well-documented and explicitly even standardized against in POSIX, but they still failed to implement this in a way that is both evidently sane and also otherwise generally accepted to be the correct way to do things ... and then they even pretended that it's somehow not actually a bug.

Those are two somewhat recent examples I can think of, but there have been many more showing the same kind of attitude.

They are ignoring hard-earned knowledge on how to do things securely, safely and reliably, they ignore the intentions of abstractions, and they pretend that obvious bugs aren't bugs because there is some weird way to reinterpret the bug into being correct behaviour (that noone expects and that causes harm).