The first saving opens a background session for file upload. That background session is kept open for future saves/uploads. No password is remembered.

Version 5.9.2

WinSCP retains the user password when saving a file, even if the check box for remembering the password for this session is not checked. After entering the password to save a file once, subsequent saves are made without a password prompt.

Steps to reproduce.
1. Establish a connection by logging in with your password but don't check the check box to remember the password for this session.
2. Open a file within WinSCP, modify the file, and save that file. Enter the password when prompted but leave the check box to save the password for this session unchecked.
3. Open another file within WinSCP, modify the file, and save that file. The file will be correctly saved without prompting the user for a password.