assert Assert(not FSavedSelection) of CustomDirView.pas 2916

I use WinScp v4.1.6. Assert Assert(not FSavedSelection) of CustomDirView.pas line 2916 occurred when one file transffering is not finish but another file transffering start. But I didn't see any syncrhonization mechanism to prevent this situation occurr.

First, this is support forum for USERS of WinSCP.
I'm not here to learn you programming.
Then I have no idea how you can make WinSCP start another transfer without finishing the first.