DethStryke
Explorer
The Situation - I'm running a mid-high level game (~13th right now) in which I inherited some interesting PCs from previous DMs - I'm not responsible for the builds or equipment of these. 
Three of the primary players (i.e. the ones that show up every week) are a Paladin of Heroneous, A redeemed 1/2 orc Monk with Vow of Poverty, and a dwarven defender.
The dwarven defender has a very powerful rod (waaaay too powerful, but that's my opinion) which, among other things, can cast Polymorph as a 20th level caster. Beset by Driders atop ~20'-tall shaped stalagmites, the dwarf decides to move to the center of the kill zone and cast polymorph on himself. He chooses the shape of a Hill Giant.
I am amazed. Other players literally call him out as a traitor to his own race.
My dilemma - what is a fitting punishment to this crime against dwarven culture? Information regarding Dwarven Defenders is VERY sparse, but it's my opinion that no dwarf would consider changing themselves into the shape of one of their hated enemies; especially one that is supposed to be the paragon of dwarven culture.
However, the game is supposed to be fun. His "mistake" is begot from power gaming - it was the largest thing he could change into, I think. I don't want to destroy his character, per-se, but I'm not inclined to let power-gamers run rampant with clauses and loop-holes.
The first idea I thought of is to have all of the Ex. powers of the prestige class to stop working; showing Moradin's displeasure at his choice. I see the prestige class as a dwarven paladin, and this would create a fall. Atonement and some quest could restore these powers, but it's not something he's going to be able to clear by just saying "I'm sorry".
What do you think and how would you resolve the scenario?

Three of the primary players (i.e. the ones that show up every week) are a Paladin of Heroneous, A redeemed 1/2 orc Monk with Vow of Poverty, and a dwarven defender.
The dwarven defender has a very powerful rod (waaaay too powerful, but that's my opinion) which, among other things, can cast Polymorph as a 20th level caster. Beset by Driders atop ~20'-tall shaped stalagmites, the dwarf decides to move to the center of the kill zone and cast polymorph on himself. He chooses the shape of a Hill Giant.
I am amazed. Other players literally call him out as a traitor to his own race.
My dilemma - what is a fitting punishment to this crime against dwarven culture? Information regarding Dwarven Defenders is VERY sparse, but it's my opinion that no dwarf would consider changing themselves into the shape of one of their hated enemies; especially one that is supposed to be the paragon of dwarven culture.
However, the game is supposed to be fun. His "mistake" is begot from power gaming - it was the largest thing he could change into, I think. I don't want to destroy his character, per-se, but I'm not inclined to let power-gamers run rampant with clauses and loop-holes.
The first idea I thought of is to have all of the Ex. powers of the prestige class to stop working; showing Moradin's displeasure at his choice. I see the prestige class as a dwarven paladin, and this would create a fall. Atonement and some quest could restore these powers, but it's not something he's going to be able to clear by just saying "I'm sorry".
What do you think and how would you resolve the scenario?