when using the -metadata parameter in windows 10/powershell terminal, I get an error

[ghost]

see below

C:\Users\myuser> ffmpeg-bar -i "input.mkv" -map_metadata -1 -vcodec copy -acodec copy -scodec copy -metadata:s:s:0 language=eng "output.mkv"
language=eng: Invalid argument

Things I've tested:

• If I replace ffmpeg-bar with ffmpeg, it works fine.
• If I run the command above using cmd, it works fine.

Any ideas on what could be wrong? Thank you.