From Accepted answer shouldn't be sorted to the top when sorting by Newest or Oldest. and accepted answer always first for oldest answers, I know that the accepted answer appearing at the top is by design. I can deduce also, that there is some kind of desire for some members to see the accepted answer in the flow of time (as it is the case for me).
So my suggestion is as follow: Why not give the possibility to the user to switch in and out the accepted answer in the timeflow, when sorting by oldest/newest? For example with a checkbox in the preferences, or at the side of the question?