My experience is that this works fine on my iPad running iOS 5.1.1, but returns TRUE every time on my iPod running iOS 6.1.3. I registered it as an error with Apple.
Update: omz is right. As soon as I downloaded the Apple dictionary on my iOS6 iPod, it correctly checks the word. It was so long ago that I installed iOS5 on my iPad. I had no memory of whether I installed it manually or if it was done for me. Despite this, this method requires manual installation on iOS6.
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