Heroism duration not doubled by GSF Enchantment

[Conveymancer]

I play Sven Stigsson, a  level 7 sorcerer with GSF Enchantment. According to the wiki, Heroism's duration should be 2 rounds/level:

GSF: Enchantment: Increases duration to 2 rounds / level.

However, I tested this, and the duration was only 7 rounds.

[Conveymancer]

This is still the case. Selfishly bumping this because my character has this spell and it would be nice if it lasted longer.