Thanks for your report.
I have sent you an email with a debug version of WinSCP to the address you have used to register on this forum.

No other prozess ist running that does that.
I configuring WinSCP to use custom folder for temporary files.
If i watch the prozess and i close the WinSCP-sourcewindow after downloading to tempfolder is finished (in right moment), the files keep in the tempfolder and WinSCP-destinationwindow can copy all files to server B. WinSCP deletes the files, i think so. If i leaf the sourcewindow open, the files will be deleted and the prozess fails.

Why do you think it's WinSCP that deletes the files?
Isn't it some other process that does that?
Did you try configuring WinSCP to use a custom folder for temporary files, instead of the system temporary folder?
https://winscp.net/eng/docs/ui_pref_storage

Hello,
sorry, my english is not very whell, but i hope you understand me :-)
i'am using winscp to copy files between two servers.
server A is connected via ftp, server B via ssh.
drag & drop setting is "use temp-dir". winscp runs in two windows (explorer-mode).
now, i drag & drop files (and directories) from server A to server B. winscp starts to download all files into the temp-folder. after download is finished, winscp begins to copy the files to server B. the problem is, winscp delete the temp-folder automatically befor copyed all files to server B. all settings i tested have no effect. how can i disable temp-folder-auto-delete?
great thanks for help!