WinSCP corrupts .mkv EMBL header on multiple file upload.

When attempting to upload a folder of MKV files the .mkv EMBL header at pos 0 is written as a null byte. As reported when attempting to transcode using ffmpeg.

[matroska,webm @ 0x55ff4c9ad740] 0x00 at pos 0 (0x0) invalid as first byte of an EBML number
[matroska,webm @ 0x55ff4c9ad740] EBML header parsing failed

Attempting to run the orginal file that was uploaded works. But downloading the file uploaded reports the same error on the PC that uploaded the file.

Uploading the .mkv file by itself, works fine. Both download & uploading of the file, and transcoding and playback on the server & original pc.

Do you men that if you upload a single file, it transfers correctly? But if you upload multiple files at one, they get corrupted? Please post session log file for both scenarios.