VERY STRANGE, cloned folder, files disappeared

I can not find solution online, even in other languages,
I wrote in different forums ..never seen this problem before!

issue:

folder (D:\folder)
suddenly it "splits" in two folders, like something cloned it
and the two copies are "locked"

on explorer I see:
D:\folder
and
D:\FOLDER

same name, in uppercase and lowercase,
both locked (padlock visible from explorer).

if I try to enter I get "Access Denied."
i tryed to unlock the privileges of the entire HardDisk

Folders are now unlocked
but both contain only one folder
called "new folder" .. that is empty.

Another strange thing:

if I delete the "new folder" from one of the two folders "cloned"
this is automatically deleted from both folders

I've tried to use Recuva, files that were inside are not deleted.
i can't find those files anywere! 50gb or more lost don't know where.
incredible
sorry for my bad english

solved.
i deleted one folder
(the uppercase one)
the other folder showed magically all the files.
WHAT THE HELL HAD DONE THAT ISSUE???
..incredible
i spent all night awake to find a solution without success,
writing in several forums


Anyone? what can provocate this issue?