It happens to Mac users too!
When I was SM for a B&M Mac store, this was a common complaint. Usually expressed as “I was dragging a {folder or file} and suddenly this OTHER folder just disappeared! Now BOTH are lost!”
The User would start to drag a file or folder, then ‘bounce’ the lone mouse button while pointing at some other folder, which acted as a “Drop” and a “Pick Up For Dragging” in the same moment.
It’s impossible to fix without seeing the screen, since you can’t see what they were dragging over.
IF the “Undo Move” command failed (or you did other things after your accident), you’ll have to get in there and slog through it file-by-file.
The only possible Good News is, if you stopped the process early enough, there probably aren’t any deletions in the Source Folder. Unless the process has changed in 8.1, the order of business is Copy, Verify, THEN Delete the source. As Chloe mentioned, very little of any consequence changes from one version of Winders to the next (new makeup, same old pig)…
I am notorious for making many copies of everything. Cleaning up my messes is quite a chore! I found a program called Duplic8 which works very well. It is slow as {insert very-slow metaphor here} but it deletes to the Recycle Bin so you have an “Ooops” up your sleeve.
If Windows denies you access to the ‘bad’ folder, you may need to take Ownership (and Full Control) of it under Properties. That’s for another post, as it’s non-trivial.
If Duplic8 (or any other duplicate file finder) doesn’t fix it, LMK & we’ll move on to Round 2.
Good luck!
PS: Top Tip for drag-n-dropping: Use the Right Mouse Button (or “Alternate” if you prefer to call it that) so than when you Drop, you get a Menu which lets you choose “Move”, “Copy”, or my favorite, “Cancel”.