I wonder if we could have IDE features that will make #2 less likely. Eg marking some lines of code that they're similar to lines of code elsewhere. And if you then change it in one place the IDE will remind you about the others.
JetBrains has something like this in their tools. It pointed me in the right direction a couple of times when touching code that is similar to something elsewhere.
Relying on your IDE to maintain program semantics is terrible. IDE should help you write good code that you commit, not be a crutch for writing bad code.
People in the thread are arguing that it's not necessarily bad code though. Also, the point of the IDE would be to help you just not forget to change it.
