Rune Chain Spell not working - after selecting friendly troop

[pouet]

I just try the rune chain spell and it's very strange, i don't think it's working as intended.
For example, it collects 4 runes from my griffins and it says "damage +200%" (50% per rune), then on the enemy target it says 2700 damage (the spell has a base of 1800 for me).
Next i try with the soothsayers, it collects 5 runes and says "damage +250 %" , then on the enemy it says 9000 damage and effectively did 6300 damage.

edit: ok i just try again and it worked as intended (collects 4runes, +200% damage and did effectively 1800*3 damage). It's erratic!

edit2 : it seems to deal the right amount of damage after all, it's just the display above the target ("xxx damage, kills : xxx) that is wrong sometimes.