By the way I guess it's a Parrot thing. So all other languages run on Parrot will suffer as well?

No, it's not a parrot thing, and tye's wrong on this. A sweep for dead objects only touches the object header arenas and those areas of the heap that belong to active objects and can contain pointers to other object headers. Those memory areas are generally segregated from the areas of the heap that contain non-pointer data such as strings.