Ad aspera

Ice Blade [4]
Each attack deals an additional (SM*5) percent of cold damage and has a chance (will vs. will) to freeze the enemy for two turns. 100.

How long does this buff last? Or is it supposed to be a sacred weapon effect that was accidentally recorded as a spell? Is the additional damage calculated based on the final value or separately from the strength multiplier?

Added 1 minute ago
Is the additional damage of sacred weapons (like those of Malabar and Igorroth) multiplied by strength bonuses or calculated separately?