Elven Branched Spear is not being treated as a Weapon Finesse weapon

In creating an unchained elf rogue for 1st ed Pathfinder, I took Heirloom weapon (from Adventurer's Armory) as a trait for my character, and chose Elven Branched Spear to give him proficiency. Since per the description "You can use the Weapon Finesse feat to apply your Dexterity modifier instead of your Strength modifier on attack rolls with an elven branched spear sized for you, even though it isn’t a light weapon," I should be able to apply my Dex modifier to attack rolls, this is not being calculated correctly. In addition due to Finesse Training I should be adding my Dex modifier to damage rolls as well, and this is not occurring either.