"no subtitle" shows first subtitle

[p-m]

Hi,
I use vdr-2.6.7 with vdr-plugin-softhddevice-2.3.1 and vdr-plugin-mpv-1.8.3.
When playing an MKV-file with the MPV-plugin and selecting "no subtitle", the first subtitle is displayed.
How could I prevent the display of any subtitle please?
TIA for any help, Peter