Why is Mathf.Pow( <some float value>, <some value less than 1> ) returning NaN on iOS 4.2 beta?

I'm having a weird issue with people running iOS 4.2 beta (presumably on iPads).

The long and short of it is because this line of code that worked before now is returning zero:

percentageToWin = Mathf.Lerp( ( 1.0f / 3.0f ), .75f, Mathf.Pow( levelNumber / 85.0f, .333333f ) ); 

(Where `percentageToWin` is a float.)

I broke it down to this bit

Mathf.Pow( levelNumber / 85.0f, .333333f )

returning `NaN`. `levelNumber` is positive. I've searched for anything regarding Pow returning NaN, and haven't found any similar issues. This math is somewhat important to the balancing of our game, and I'm not sure how to work around it.

For reference, the game was compiled against Unity iPhone 1.7. I'm going to try it with Unity 3 to see if it goes away, but somehow I doubt it.

Has anybody seen any similar issues or have any solutions?

So I made a test project with my current Unity iPhone 1.7 as well as the latest Unity 3.0 iPhone that is nothing more than a scene with the default camera and a script that does this:

void OnGUI()
    GUILayout.Label( Mathf.Pow( 8 / 35.0f, .333333f ).ToString() );

Running the app built with Unity 3.0 spits out the correct number. Running the app built with Unity iPhone 1.7 spits out NaN.

For now I'm just going to file a bug report and try to get our project built with the new version of Unity (which is going to be a pain because of all the project settings, etc).