Unexpected behavior when casting away immutable

[Mike Parker via Digitalmars-d-learn]

I have a situation where I would like to demonstrate violating 
the contract of immutable (as an example of what not to do), but 
do so without using structs or classes, just basic types and 
pointers. The following snippet works as I would expect:

```
immutable int i = 10;
immutable(int*) pi = &i;
int** ppi = cast(int**)π
writeln(*ppi);
int j = 9;
*ppi = &j;
writeln(*ppi);
```

Two different addresses are printed, so I've successfully 
violated the contract of immutable and changed the value of pi, 
an immutable pointer. However, this does not work as I expect.

```
immutable int x = 10;
int* px = cast(int*)&x;
*px = 9;
writeln(x);
```

It prints 10, where I expected 9. This is on Windows. I'm curious 
if anyone knows why it happens.