Closures referencing immutable variables declared inside a loop can observe how these immutable values are changing - this should be impossible according to the definition of "immutable".

$ cat closure.d
import std.stdio;

void main() {
    void delegate() res;
    foreach (i; 0..2) {
        immutable v = i;
        void printi() {
            writefln("ptr=%x value=%d", &v , v);
        }
        if (i == 0) {
            res = &printi;
            res();
        }
    }
    res();
}

$ dmd closure.d
$ ./closure
ptr=b75bae44 value=0
ptr=b75bae44 value=1

As you can see, an immutable variable changed its value. The code above is SafeD clean, i.e. doesn't use any dirty tricks that would subvert the typesystem. (Except printing the pointer address, which is just for demonstrating that it's the same value.)