Cloning delay gets worse and worse - Macromedia Director 3D

[RavenWorks]

In my project, I clone and delete a lot of models (bullets) almost constantly.
The system has no trouble handling that number of models in the world, yet for
some reason, as the project runs, there starts being a noticeable delay
whenever something is cloned. In under a minute, the game is slowed down to
incredible choppiness whenever something needs to be cloned, even though the
total number of objects in the scene is roughly the same (sometimes lower).
More importantly, this delay does NOT happen if I make new models instead of
cloning. I have already checked and as far as I can tell, I am disposing of all
the models appropriately. (And even if I wasn't, switching to newModel wouldn't
make the symptoms go away if that was the problem.) How can creating,
parenting, and adding shaders to several models be faster than cloning one?
(Even if it is, why would cloning an object take longer and longer as the scene
continues?)

In short, am I doing something wrong when I clone, or is this a flaw inherant
to cloning and I should be avoiding it and using newModel instead?

[RavenWorks]

I hate to just bump a thread like this, but not being able to clone objects is
really complicating my projects... Is this a known issue? Is there anything I
can do? Why is cloning so quick at first, but so bad as time goes on?