Consider the following test case for js shell: var setter_was_called = 0; this.x setter= (function() { setter_was_called++; }); this.watch('x', function() { }); x = 1; if (setter_was_called !== 0) throw "Unexpected setter call"; Currently it throws an exception as setting the watch point on a property with a setter caches the setter and triggers calls to it even after the property is deleted. This is related to bug 394964 but the problem here is different.