Used to work in DT2.
Repeat by:
(1) Given open database with folders and sub-folders in side bar
(2) Drag item from inbox to {DB}/folder and hover…
(3)…revealing further sub-folders
(4) Continue the drag operation, targeting a sub-folder
(5) Release, to conclude drag operation, resulting in moving item from inbox to {DB}/folder/sub-folder
(6a) In DT2, after releasing, the revealed hierarchy will close back up again, reclaiming valuable screen space if someone has, say, lots and lots of folders marching down the side bar
(6b) In DT3, hierarchy remains (annoyingly) open, causing more mouse clicks and scrolls later when one has to find other things in the hierarchy
Alan