When you are only seeing this behavior with truehd tracks then this sounds like you are very likely suffering from the same issue described here => Dolby TrueHD passthrough - modified mpv build
Maybe you can try such a modified mpv.dll and test again?
VLC does not show this issue because it uses a very outdated version of ffmpeg (last time i tested vlc), before changes were made to the truehd passthrough logic.
