I'm not sure whether this is new behavior on .255, since I've never tried this before.

(1) I designed a soldier with a short sword, built 4 of them, put them in an army, and attacked a troll.  The result was victory, with the troll and one of my soldiers killed. Afterwards I had 3 soldiers on the same square, not in an army.  I had to move them into another square to form them into an army again.

(2) Using the same type of soldiers as above, I put 2 of them in an army and attacked a spider.  Again, victory, with the spider and one of the soldiers killed.  Afterwards, two soldiers were on adjacent squares, one where the battle was, the other one square south.  I could select and move the one where the battle was, but could not select the other one.  Although killed, he remained as a ghost, not moving and not selectable.  Which maybe was appropriate since I'm playing on Halloween.

If an army is associated with a leader and dissolved when the leader is killed, then perhaps (1) is not a bug, but I think I'd prefer to have the army automatically reform with a new leader.  (2) seems like a definite bug, though.