What can be wrong??
Almost anything:
  • You could be reading a file other than the one you think you are.
  • You could be reading a file that is being appended to by another process, so by the time you check the file is has more content.
  • You could be reading a binary file where the concept of "line" in meaningless.
  • You could could be reading a file with old-style Mac OS line endings expecting these to be treated as line endings.
  • You could just be mistaken about what is actually read.