To what extent does the Shield Master feat ignore penalties?

Question

Reference:

Shield Master (Combat)

Your mastery of the shield allows you to fight with it without hindrance.

Prerequisites: Improved Shield Bash, Shield Proficiency, Shield Slam, Two-Weapon Fighting, base attack bonus +11.

Benefit: You do not suffer any penalties on attack rolls made with a shield while you are wielding another weapon. Add your shield's enhancement bonus to attacks and damage rolls made with the shield as if it was a weapon enhancement bonus.

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I can think of several penalties...

1. Does this cover the penalty to attacks with Power Attack?
2. Does this cover the penalty to attacks with two-weapon fighting?
3. Does this cover the penalty to attacks while fighting defensively?
4. Does this cover the penalty to attacks using Combat Expertise?
5. Does this cover iterative attacks with Improved Two-Weapon Fighting?

See where I'm going with this?

Question

Does this essentially make all attack rolls with your shield in your off-hand at your full bonus to attack?

Answer 1

By strict rules as written, you are correct. The feat is written poorly and has been discussed ad nauseum on the official Paizo forums, with many folks arguing both sides. There are two factors to consider that allow you to clarify the intent of the feat.

First, removing all penalties to hit provides an overly large benefit in comparison to other feats. Most GMs would agree that this is clearly out of line and would not read the feat this way or allow players to use it in this fashion.

Second, (and perhaps more importantly) there is a feat table in the Pathfinder RPG Core Rulebook where this feat was originally printed. I've provided a tiny excerpt of the table below, where the Shield Master feat is listed (pg 116 in the 5th printing). You'll note that the condensed benefit for the feat is listed as "No two-weapon penalties when attacking with a shield". While this benefit description is by no means the be-all-end-all rules source for the feat, it does clarify the intent of the author.

For the two reasons above, it is likely that this feat was only intended to remove the two-weapon penalties when attacking with a shield along with another weapon (options 2 and 5 from your list above).

EDIT: Thanks to SevenSidedDie for bringing to attention the fact that we also now have an official FAQ Answer on this topic which reads:

Shield Master allows a character to ignore the Two-Weapon Fighting penalties on attack rolls with a shield while wielding another weapon, but not any other penalties.