You may have Folder Content Detection turned on, and the 9 directory has logs of images which cause it to switch to thumbnails.
Or you may have saved an explicit folder format for the 9 directory which is overriding the one you're saving for D:. (Or the one for D:\ may not be set to apply to subfolders.)
I recommend going through the Folder Formats: Quick Guide, which explains how to get the same format in all folders, or the Detailed Guide if you want something more complex.
Note that hovering the mouse (don't click) over the format lock icon on the status bar will display a tooltip which tells you where the current view settings are coming from. (The Detailed Guide I linked just above explains this in more detail and has a screenshot.)