All of the related objects in DMZ are created via PHP magic methods. Actually, a lot of the stuff is magically generated. This has several very important benefits:
1) You don't waste memory and time creating unused objects.
2) You avoid infinite recursion ($user->usergroup->user->usergroup->user->...)
3) Autoloading is more intelligent - the objects are only auto-loaded the first time you access them.
The side effect is that many of the properties of a DMZ model are not visible to debuggers until the first time they are used.
Also, I haven't actually gotten a proper PHP debugger set up yet (I know - shameful), so I don't know if there are limitations [in the debugger].