Consider the following text:
[C++11: 12.4/11]: Destructors are invoked implicitly for constructed objects with static
[C++11: 12.4/11]: Destructors are invoked implicitly
[C++11: 12.4/11]:
It's that B's destructor is generated by the compiler at the line of your error and it has a call to A's destructor which is deleted, hence the error. In the first example nothing is trying to call A's destructor hence no error.
B
A