Weapons, Two-Handed in One Hand: When a feat or other special ability says to treat a weapon that is normally wielded in two hands as a one handed weapon, does it get treated as one or two handed weapon for the purposes of how to apply the Strength modifier or the Power Attack feat?
If you're wielding it in one hand (even if it is normally a two-handed weapon), treat it as a one-handed weapon for the purpose of how much Strength to apply, the Power Attack damage bonus, and so on.
Remember being treated as a One Handed Weapon is not the same as being wielded by one hand.
As Per One Handed weapon quality:
One-Handed: A one-handed weapon can be used in either the primary hand or the off hand. Add the wielder's Strength bonus to damage rolls for melee attacks with a one-handed weapon if it's used in the primary hand, or 1/2 his Strength bonus if it's used in the off hand. If a one-handed weapon is wielded with two hands during melee combat, add 1-1/2 times the character's Strength bonus to damage rolls.
This FAQ was aimed at the cases where certain class features or feats changed a certain Two Handed Weapon into a One Handed Weapon.
Examples:
Thunder and Fang (Combat) Benefit: You can use an earth breaker as though it were a one-handed weapon. When using an earth breaker in one hand and a klar in your off hand, you retain the shield bonus your klar grants to your Armor Class even when you use it to attack. Treat your klar as a light weapon for the purposes of determining your two-weapon fighting penalty.
As per the description of the One Handed quality, you only get the +50% increase if using both hands.
Now the first FAQ:
Power Attack: If I am using a two-handed weapon with one hand (such as a lance while mounted), do still I get the +50% damage for using a two-handed weapon?
The question specifically targets Two Handed weapons which have an ability to be wielded in one hand but are not reclassified as One Handed weapons, such as the Lance.
Yes at first glance it can seem confusing because often times it is forgotten One Handed is a weapon quality that also doubles as a description of how a person is wielding it. Wielding a weapon one handed is not the same as wielding a One Handed weapon.