China DOS Union

I used md at the cmd prompt to create a cai folder on drive E, then created another cai folder inside the cai folder, making it e:\cai\cai like that.
Later I used the rd command and entered rd /s cai in cmd. After confirming, the cai folder was still there, and it couldn't be opened anymore. It said access denied, and it couldn't be deleted either.
Wasn't using rd with /S supposed to delete cai together with the cai folder inside it too? Why is it still there, and why did this problem happen??
Please, could an expert help me!! Thanks!!

After restarting the computer, the folder was gone. I don't know why. Does anyone know why rd /s cai didn't delete the folder and subdirectory together? They were all empty. Why did that folder still remain right after the deletion succeeded, and then it couldn't be deleted again? But after a restart it was fine. I just can't figure it out.

Please explain the environment, and check whether the system is clean.

Ugh, it was fine after a restart, but I don't know why?????????