This is still a problem; every once in a while I see questions closed as duplicates because people didn't see the difference, sometimes even after it was pointed out in a comment.

A particular form of this that I would ask everyone to try to avoid is closing a question that asks about the error in a calculation as a duplicate of a question asking for the correct calculation. Understanding what went wrong with one's own calculation is much more helpful than being pointed to a different, correct calculation. If the question specifically asks what went wrong in a specific solution attempt, it's a completely different question from one that asks for a solution of the same problem. This question (which was closed as a duplicate and then reopened) is an example.

This is still a problem; every once in a while I see questions closed as duplicates because people didn't see the difference, sometimes even after it was pointed out in a comment.

A particular form of this that I would ask everyone to try to avoid is closing a question that asks about the error in a calculation as a duplicate of a question asking for the correct calculation. Understanding what went wrong with one's own calculation is much more helpful than being pointed to a different, correct calculation. If the question specifically asks what went wrong in a specific solution attempt, it's a completely different question from one that asks for a solution of the same problem. This question (which was closed as a duplicate and then reopened) is an example.