Thanks for your report.
I will take a look at this issue.
I am not sure if this is known bug , but just wanted to throw it out there..
the version I have is 5.1.7(Build 3446)
Steps to reproduce
1) Connect my PC to a remote server through LAN
2) Disconnect the LAN
3) Try Re-connecting the LAN
4) immediately after reconnection , try to drag and drop the file from your PC to remoteServer ( Make sure the file already exists in the remote Server
5) WInsCP hangs for a couple of seconds and then asks "Abort" "Reconnect" "Cancel "
6) Click Re-Connect
7) The file that we intended to move successfully moves to the remote server without actually asking if you wanted to overwrite the file ( Because the file already Exists)
8) This case does not happen if WinSCP has been in good connection . ( There is always a popup if I want to overwrite the exisiting file
So there you go
if you cant reproduce you can contact me at email@example.com, I'ill send a video or something..