delete makes the memory available for later requests via new. Whether or not it scrambles to content is undefined. Since it is faster to leave the contents as they are, in release mode it will probably appear that the memory is still "available". In debug mode, it might get scrambled with magic numbers.
What you're experiencing here is called "undefined behavior" in C++. In this case, the undefined behavior is caused by accessing a piece of memory after its lifetime has ended. Just don't do it.
