ah okay ! thanks for the explanation !
Tags are not a good idea then, because think of the following scenario :

you assign an object as tag to entity#1, then you are c_tracing and hit entity#1 and want to access its tag object -> but this won't work, because the object that you retrieve via c_trace is a new object (although it points to the same memory location and thus 'is' the entity#1) and doesn't have a tag !

edit :
a 'tag' could be simualted simply by a "Dictionary<IntPtr, object> tagObjects" where you can get the unique entity identifier by someEntity.getIntPtr() !