The directory above scroll works fine you can place your pointer on it and drag shouldn't the thumbnail scroll work the same way, where you grab it and it scrolls, this is very odd behaviour? I think to keep it consistent it should work the same as the directory.
No. It shouldn't work the same way. When you are scrolling folders, you only have to display text. When scrolling thumbnails, it has to display images realtime. If it tried to update and scroll those while dragging, the scrolling would lag and prevent you from scrolling (for example) to the bottom of the list quickly. It wasn't made for that. If you want to scroll in the manner you suggest, just click above or below the scroll knob to scroll a page at a time.
Regards,
Mike