$ cat heisenbug.js 
function heisenbug() {
    var a;
    function f(b) {
        if (a) console.log(a === b.c ? "PASS" : "FAIL");
        a = b.c;
    }
    function g() {}
    function h() {
        f({
            c: g
        });
    }
    h();
    h();
}
heisenbug();
heisenbug();

// if following line is commented out then rollup generates an empty chunk
//console.log(123);

$ cat heisenbug.js | node
PASS
PASS

$ cat heisenbug.js | rollup

- → stdout...

(!) Generated an empty chunk