CreateWritableClone and Dynamic properties

I have one dynamic property, let's call it globalProp.
I'm changing the content by code like this:

PageData NewPage = CurrentPage.CreateWritableClone();
NewPage.Property["globalProp"].Value = "Test";

But the dynamic property is always null (don't exists)... Even if I fill it with content manually in Edit mode.

Is the function CreateWritableClone not handling dynamic properties at all? And what to do if I want to manipulate those by code?

Regards, Andreas Ek, Internetfabriken.