It's a little hard to describe precisely the steps that lead to the problem, since I cannot reproduce it easy.
I suppose that it was related to the integration with other applications.
More precisely, I have some special non-text "editors" registered for some binary types, e.g.:
7zFM.exe for the *.zip;*.jar;*.ear;*.war;*.rar;*.aar extensions list
or
jd-gui.exe for the *.class one
It is possible that after pressing F5 to download such a file (it was a jar one of approx. 3 MB), I've accidentally press Enter, too, which triggered the editing action on that archive file. (It's not clear if it the editing was on the original (remote) one or on the copied (local) one.)
==============================
Auto-generated message bellow:
==============================
WinSCP 5.7
Error message:
Invalid access to memory.
Stack trace:
[01348703]
[01B205DE]
[01B22646]
[01B1F5C0]
[77A06A86] ntdll.dll
[779D013E] ntdll.dll.KiUserExceptionDispatcher
[0137DCBB]
[0134887E]
[01A4C4BD]
[019875A7]
[01A609F9]
[0134D30F]
[0134DF18]
[0134DF9F]
[0134E0D7]
[01372F3A]
[016C2740]
[014AA2A1]
[01B20C49]
[01B22223]
[019873FC]
[01A609F9]
[0134D30F]
[0134DF18]
[0134DF9F]
[0134E0D7]
[01372F3A]
[016C2740]
[014AA2A1]