Insert Catchy Title Here

Reflection?

Reflection wouldn't help, the field is marked as readonly.
Can you reproduce this issue? Looks like a CLR bug.

You can set that[accidentally] to null in the constructor for that class...

Is this a proxied instance?

This particular class has no defined constructors, just relying on the default public constructor.

That breakpoint is hit during deserialization of a WCF call. My only guess is something along the lines of FormatterServices.GetUnintializedObject.

Seems like the order with maybe something in the CLR or something? Like the object hasn't been instantiated yet, but you're trying to set it. So the set method it looks like is being called before the object is created. Course, no idea how that could really happen, but maybe something with a difference in a List<T> to T[]? Instead of having the instantiation in the class, try setting it directly in the ctor instead? Just guessing :P