This

$ptr=\$hash{'name'}
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Is a reference to the value of the element of %hash named 'name'. All your code does after you take that reference is add new elements to %hash. The value of $hash{name} doesn't change, so it doesn't move.

But even if you changed the value of $hash{name}='fred';, the value you previously assigned to $ptr would not change as a result, and it would still point to the original value. Indeed, the original value will remain where it is and not be garbage collected until you assign something else to $ptr, or $ptr goes out of scope and is itself GC'd.

To get an understanding of the internal structure of Perl's datastructures work at the C-level, take a look at Gisle Aas' amazing Perl Guts Illustrated.

The main thing to note though, is that Perl's references have some superficial resemblence to C-style pointers, but thinking of them, or trying to use them in that way is not the thing to do. If you have a C++ background, then thinking of them as roughly equivalent to C++ references is a more intuative analogy, and will get you into less problems.