The problem is reportedly fixed by Windows 10 Creators Update:
https://winscp.net/forum/viewtopic.php?p=78499#78499
https://winscp.net/forum/viewtopic.php?p=78499#78499
Before posting, please read how to report bug or request support effectively.
Bug reports without an attached log file are usually useless.
My problem was resolved by installed Dell's mouse driver. I have a Dell laptop, and for some reason it had a Microsoft driver instead of Dell's.
I'm having the same problem. I can upload/email a video-recording of the issue if you'd like.
Brent