I remember reading about this before, but I can't find anything on it.
If you have a party of units that is damaged in a fight, its graphical representation will reduce as men are killed. If you heal the unit WITHOUT QUITTING, those units will return as the HP is regained.
If, however, you save the game, quit, and reload, then when you resume playing the party will be permanently reduced into a smaller unit size and cannot recover HP up to its old maximum.
One way or another this is a bug. Either parties should not heal back up to full strength or they should not be reduced permanently just because I save and quit the game.
Does anyone know the answer?