While testing collections of links, I found a difference in behaviour between removing an object and invalidating it. LnkLst/LnkSet hide invalidated links but Lst<Mixed> and Set<Mixed> do not have this capability. If a link in these collections is invalidated it becomes null and the size of the collection is not changed. Furthermore, the stored link is not a true null because operations like find_first(Mixed{}) will return not found.

T link_collection = {object};

T                   object.invalidate()     object.remove()
LnkLst              {}                      {}
Lst<Mixed>          {null} <--*             {}
LnkSet              {}                      {}
Set<Mixed>          {null} <--*             {}
Dictionary<Object>  {key:null}              {key:null}
Dictionary<Mixed>   {key:null}              {key:null}

I think the easiest thing to do here is to remove the links from these collections instead of storing a link to the invalidated object.