The problem happened several times, but I am not able to reproduce it anymore. I have logging enabled now, next time the problem occurs I'll get the log and reopen this case.

From the log:
Server version: SSH-2.0-OpenSSH_3.7.1p1
We claim version: SSH-2.0-WinSCP-release-3.5.6

Winscp version 3.5.6 (was mentioned in first message as well). I have not tried 3.6 given that this version is still beta.

abakker wrote:

The remote system is a Unix system, but I do not know which manufacturer/OS version. Protocol in use is SFTP (v3). I hope this info is enough.

Thanks. Give me at least manufacturer of the SSH server. You'll find it in the session log as "Server version:".
And also, what version of WinSCP do you use? Have you tried the latest one?

Server information:
. SSH protocol version: 2
. Encryption algorithm: aes
. Compression: no
. File transfer protocol: SFTP (v3)
Protocol information:
. Can change permissions: yes
. Can change owner/group: no/no
. Can execute arbitrary command: no
. Can create symlink/hardlink: yes/no
. Can lookup user groups: no
. Native text (ASCII) mode transfers: no
The server does not support any SFTP extension.

The remote system is a Unix system, but I do not know which manufacturer/OS version. Protocol in use is SFTP (v3). I hope this info is enough.

What protocol SCP or SFTP? What is the operation system on the server? What is the SSH server (OpenSSH, ssh.com, etc.)? If SFTP, what version?

I select multiple files on the remote system (ctrl click), and change properties to 604. All files are processed, but in the end the protection has not changed (from 600 to 604). Version 3.5.6. Am I doing something wrong or is this a bug?