Rage has no effect on ancient creatures.

playing as Outcast, Kilgor (A51, D26) vs. Kal'Kh (A24, D26). Final battle, siege. After exchanging the remaining stacks, I had 20 gray bears left, and my opponent had 37 devils. Both were under air protection, and there were no other buffs/debuffs. The devils, under Berserk, fly towards my bears. The bears can kill 15-23 of them. I cast Frenzy on my bears, and... the damage doesn't change. The same range of 15-23, but with zero defense. We hit for 20, received a counterattack. In the end, my opponent won, although even he said after the battle that it was 100% my victory. For comparison, here's a video with a similar situation (link to the exact time): https://youtu.be/oKvvkXUQqD8?t=2548
Here, Frenzy works as it should. I checked it in hot-seat mode - it's the same. What's the catch? Where does this error come from?