Why does my fighter have the option to pick the Martial Weapons feat if he already has it?

Perhaps it's the Weapon Specialization?

I assume thats what its for but it does not say the benefits if any... My fighter has martial weapons proficiency all, then for another feat i can select martial weapons proficiency and specifically pick a weapon. I looked up weapon proficiency in the manual but it did not mention this. this is all it says.

Martial Weapon Proficiency [General]
Choose a type of martial weapon, such as a longbow. You understand how to use
that type of martial weapon in combat.
Use this feat to expand the list of weapons with which you are proficient beyond
the basic list in your class description.
Benefit: You make attack rolls with the selected weapon normally.
Normal: When using a weapon with which you are not proficient, you take a –4
penalty on attack rolls.
Special: Barbarians, fighters, paladins and rangers are automatically proficient
with all martial weapons

I noticed this showing up as an option for my fighters as well. I don't know why it's showing up as an option, but I'd just ignore it for those classes who already have martial weapon proficiency. It won't benefit you.