Can I rely on the LINQ ToArray() always returning a new instance?

I'm looking for an easy way to clone off an IEnumerable parameter for later reference. LINQ's ToArray extension method seems like a nice, concise way to do this.

However, I'm not clear on whether it's always guaranteed to return a new array instance. Several of the LINQ methods will check the actual type of the enumerable, and shortcut if possible; e.g., Count() will see if the method implements ICollection, and if so, will directly read its Count property; it only iterates the collection if it has to.

Given that mindset of short-circuiting where practical, it seems that, if I call ToArray() on something that already is an array, ToArray() might short-circuit and simply return the same array instance. That would technically fulfull the requirements of a ToArray method.

From a quick test, it appears that, in .NET 4.0, calling ToArray() on an array does return a new instance. My question is, can I rely on this? Can I be guaranteed that ToArray will always return a new instance, even in Silverlight and in future versions of the .NET Framework? Is there documentation somewhere that's clear on this point?