Tactical battle : an ennemy become a friend

[Djouk]

Playing scenario 1815 as France, i defended against alliance of Prussia, Russia, England, Austria in Paris. I played a tactical battle against all this coalition. I saw Prussia, England, Austria against me on the map, but later Russian units joined me as if they were my allies. I checked in diplomacy and this seem to be a bug ! No prob when i play with immediate result of battle.