martin wrote:

I was able to reproduce the problem.
This issue has been added to tracker:
https://winscp.net/tracker/803

I'm also emailing you a link to development build of WinSCP to test.

Thanks, it works: Files are not lost any more with these settings.

One small issue seems to remain: The original creation date of a few files is sometimes lost, and replaced by the current date and time. But no data is lost.

I was able to reproduce the problem.
This issue has been added to tracker:
https://winscp.net/tracker/803

I'm also emailing you a link to development build of WinSCP to test.

Thanks for your report.
I will take a look at this issue.

How to replicate it:
1. In Transfer Settings, allow several (e.g. 2) transfers at the same time, and check "Transfer on background by default" and "No confirmation for background transfers".
2. Select a remote folder with many files.
3. For testing purposes (and so that you won't be sorry for its loss), create a local copy of it.
4. Move it to another local folder in two threads, e.g. by standing on the folder and pressing F6, Enter, F6, Enter, in quick succession. (This is a simple way to reproduce the error, but there are more sensible ways too.)

Now compare the contents of the two folders: the original copy, and the one created by moving it. Most of the time, several files will be missing from the latter.

I took the time to write because I think it is a high priority bug to fix, as it involves possible loss of data.

My configuration:
- Windows XP, with latest service packs
- latest WinSCP (4.3.6., Build 1655)

Thanks!