Drag DVD VOB files or folder to drop zone. (Does not work)

I would like to convert a DVD to play on my MP4 device, but the drag and drop feature does not work correctly.
I loaded a DVD, selected the folder, dragged it to the drop zone, and nothing happened.
Expected result: Folder shows in drop zone.
Actual result: No folder in drop zone. Drop Zone did not change.
I attempted to drag individual files with the same result..

However, using the "Add folder" button worked as expected.