Same problem here.
Act II, turn 28. I conquered the yellow general's capital in turn 27 and now he's throwing all he got left there and on my own capital.
I had played this turn once before, almost to completion, but rage-quit (Alt+F4) in the defense battle because the enemy kept running over me with bomber balloons and I hadn't researched any air units yet.
Now, when I load the saved game and enter the battle phase, the first battle works fine (I auto-resolve), but the second battle has the "Retreat" and "Ready" buttons greyed out. The card slots are also non-clickable. However, hovering over the enemy units still shows the popup and I can minimize the battle dialog or view the map.
Can't continue playing because of this, I tried loading an older save, restarting the game, but it always happens like described.
