i have always assumed that after the initial skirmish phase, where the minion loses fierce, then it comes to the regroup phase(minions regain the ability to be fierce), the fellowship chooses to move DURING the regroup phase, and moves to the next site. it never specifies that the effect lasts until the LAST regroup phase of your turn.
so i believe that in the case of double moving, the minions can regain fierce at the start of the very next regroup phase. the regroup phase which the fellowship moves during. just because the fellowship doesn't reconcile, doesn't mean its not a real regroup phase.
-mm