Initialising an array with it's subclass changes the arrays type?

Hi I was very confused for a while as to why my code wasn't behaving as expected, is this a bug or do I somehow need to be more explicit in the array definition? I would have thought the returned type should be BaseClass[] not SubClass[]? Cheers

Code (csharp):

1. class BaseClass{
2.     function BaseClass(){
3.     }
4. }
5.  
6. class SubClass extends BaseClass{
7.     function SubClass(){
8.     }
9. }
10.  
11. var testArray: BaseClass[] = [new SubClass()];
12.  
13. function Start(){
14.     Debug.Log(testArray.GetType());
15. }