I've been waiting for someone to mention this....
What you are seeing is happening because the culling is asynchronous. When you quickly scroll some items pop into view, but since a new visibility list has not been received from the culling thread, it does not draw the new objects that are in view yet. You can get the same effect with a listbox with many items or a treeview.
There are some different possible solutions for this. I could make the camera culling frustum bigger, or disable frustum culling on a per-object basis. It is probably best to get the engine in people's hands first, see how it gets used, and then decide on a solution.