Audition Manual Pitch Correction Problems

I've been using Audition to improve singing tracks for my choir.  I am going crazy using manual pitch correction. The problem is that having adjusted a section and hit 'apply' (selection only not whole track) the result is not what I input. I tried it with a simple constant tone and same result. The first changed section of the track I make seems ok. The second looks quite different from what I input.  Is it maybe applying the first adjustment to the second section?  Thereby I'm getting 2 adjustments superimposed?  If so how do I overcome this? Any advice will be very welcome. None of the online  tutorials seem to help.