Janette,
Are we to understand that you actually changed the names of the options in a multiple option single choice dropdown list question in a Feedback instance after some of the students had started to answer it?
If that is the case, then you should not surprised of the results you are obtaining. That is not a bug in the design of Feedback but only quite normal, expected behavior.
To answer your question #2, other question types would behave the same. And I would add that you would get the same results with any other similar survey software.
This is so obvious that I wonder if I have correctly understood your question(s).
Joseph