The set bonus is not broken.
While 4T10 is equipped, you will not take an extra 10% physical damage when Enrage is active, despite what that pesky buff tooltip says. Guess what? The old one said Enrage reduced armor. 4T10’s bonus text was not updated to reflect the change of Enrage. Enraged Defense will always give you 12% damage reduction from all sources of damage, including physical.
There is a simple, very effective, test for this: Have someone duel you and punch you with no weapons, trinkets, or AP increasing items(AV Rep ring) equipped. Just let him keep punching you. Take note of the amount of damage you were taking. Take that amount and subtract 12% from it (or multiply the damaging amount by .12 and subtract that value from the original). Use Enrage while getting punched. The amount of damage you’re taking while under Enraged Defense should reflect the answer you received above, which is exactly 12% damage reduction.
I used a Hunter for this experiment. I used his pet afterwards to confirm. I was getting hit for 206, meaning a 12% damage reduction would be ~181. I used Enrage, and I was getting hit for 180-182.
Again, the set bonus is not broken. All it is is a case of un-updated tooltip, which Blizzard is notorious for. You can relax, I promise.