IMMEDIATELY following opening of the program and logging in, RIGHT-Click anywhere in lower file area panes either local or remote. Has to be in 'clear' area to the right of files.
If you navigate, the problem goes away. So it has to be reproduced immediately after logging in to first site and before you navigate folders/dirs.
Invalid access to memory.
I know how to reproduce the problem or the problem happens frequently enough. I wish to be contacted by the WinSCP team to help resolving the problem.
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.