I'm just posting Steve Lionel's comment as an answer, so that I can close this question:
"The answers to your three questions are: No, No, No. But there can be many possible causes of numerical differences, especially when the algorithm is unstable. Maybe more of the code vectorizes, improvements to math routines, different order of operations, etc., etc. As others have said, if you can provide a test case to Intel Premier Support, we'll help you figure it out. But you can also work on it by seeing where in the process the results start to diverge." – Steve Lionel Apr 3 '14 at 20:17