I plugged in my Nexus7 (which does not present a drive letter) and got the attached. I did click on List first level of device and selected my GDAK folder.
Image may be NSFW.
Clik here to view.
Brian
Edit to add - I can drag and drop from windows. I can delete files with the test program, but not folders. I cannot copy files to device with test program.
Image may be NSFW.
Clik here to view.

Brian
Edit to add - I can drag and drop from windows. I can delete files with the test program, but not folders. I cannot copy files to device with test program.