[aflag]

Often times it's because there is no good solution. That is, you can't really fix the problem without being overly strict and making common use cases impossible or awkward to use. So you settle for something that usually works for most people. Bad designs have a tendency of creeping up.

The thing about things designed with bad edge cases is that they can have dire consequences for some people, but as long as it works for most people, they stick around. Forever causing pain.