Can you do this operation in 2 steps -- 1) move it to /backups and then 2) move it to the sub-directory?
Yes I can move this way. But not directly to sub folder as mentioned in original post.
And in the confirmation dialog when we move file like you said, the double slash is also not there like shown in the dialog when file is moved to sub folder.
In fact, this is not a new problem. It is prevailing since quite long in CWP and remains unaddressed unfortunately.