In LINQ, does orderby() execute the comparing function only once or execute it whenever needed?

I found a method to shuffle an array on the internet.

Random rand = new Random();
shuffledArray = myArray.OrderBy(x => rand.Next()).ToArray();

However, I am a little concerned about the correctness of this method. If OrderBy executes x => rand.Next() many times for the same item, the results may conflict and result in weird things (possibly exceptions).

I tried it and everything is fine, but I still want to know whether this is absolutely safe and always works as expected, and I can't find the answer by Google.

Could anyone give me some explanations?

Thanks in advance.