I'm not sure what you mean. Do you mean there is a bug _in the garbage collection algorithm_, if the object is not freed in the very next garbage collection cycle? Well, it depends: the garbage collection could defers collection of some objects until memory is low. Multi-generation garbage collection algorithm often do this.

You can defer the actual freeing of the object until at least one GC pass finishes. Then alert if any of them are still reachable.