AesManaged class Key and KeySize properties issue

Today when working with AesManaged class I've encountered very strange behavior.
If you have a code like this - you're in trouble:

AesManaged aes = new AesManaged();
aes.Key = key;
aes.KeySize = key.Length; //the problem

The problem with this code is setting KeySize after setting Key value.
When you set KeySize after Key - the previously specified key is discarded and a brand new key value is generated and put into Key property

I find this behavior rather strange, especially that there is no information describing what will happen after setting KeySize.

I would expect that when Key value is set setting KeySize will throw exception if specified key's size is bigger or smaller than the new one.