why only a few folders listed when saving email attachments?
 

When I save email attachments and choose SD card as the destination, the "Folder" dropdown menu has only a few of the folders on the SD card - it's not a real folder tree like in some apps, but just a flat list, and it doesn't contain many of the subfolders into which I'd like to save attached files. What am I missing - how come it's not all of them and how does it decide which ones it will show you as save-as target folders?

Mike