Of course ent_clone consumes memory. Doubling the model in memory is the very purpose of ent_clone - or for what other reason are you using it?

A cloned model is a precise copy of the original model, and everything, behavior, memory releasing and so on, is precisely the same. The engine does not know the difference between a cloned and original entity.

Imagine you have just copied the model file under a different name, and used the copy for the entity - this is the same as cloning.