I replaced someone who...let's just say didn't know half as much about certain legal responsibilities of the position she held as she thought she did. I have finally trained employees that the quickest way to insure they won't get their way is to say, "When Gerri was here..."
I remember one employee who was the office know-it-all. We didn't find out to what extent until she left the job and other departments started calling up asking who had replaced her. When I explained to them that the position hadn't been filled yet, I'd ask them to tell me what they needed and I'd figure out who could best assist them. Several of them then asked me questions that fell into MY area of responsibility all along (we had completely different jobs). When I told them that, they said "but 'Jane' has always helped me with that!" and when they told me what she'd said, more often than not it was at least partially incorrect. We finally figured out that she had a habit of answering other people's phones when they were out of the office, and instead of taking a message, she would answer their questions for them, according to whatever she thought the answer should be. The only reason we could think of that she would do that was to make herself seem more important or valuable as an employee, but it just ended up confusing a lot of people (and making us happy that she had moved on to another employer!)