I've reached level 5 and apparently as a level 5 unpredictable sorcerer my 'Flame Weapon' spell gives random elements each time it's casted.
I've casted it about six times, three times on my summoned 'Shelgarn's Persistant Blade' and three times on players, using different weapons each time.
It only gave a fire VFX and fire damage.
Ah, nevermind. After removing and reapplying it worked.