The 'Mute audio' button on the 'Volume Control' screen doesn't mute the sound

There are many OSS devices. Clicking on the 'Mute audio' button for the /dev/dsp3 device doesn't actually mute it, only shows it in UI as muted. The corresponding volume control controls the volume of that channel fine.

OS: FreeBSD 12.2

$ pkg info | grep xfce
libxfce4menu-4.14.1_2          Widgets library for the Xfce desktop environment
libxfce4util-4.14.0            Extension library for the Xfce desktop environment
xfce-4.14                      Meta-port for the Xfce Desktop Environment
xfce4-appfinder-4.14.0         Application launcher and finder
xfce4-calculator-plugin-0.7.0_1 Simple calculator for the Xfce panel
xfce4-clipman-plugin-1.6.1     Clipboard manager for the Xfce panel
xfce4-conf-4.14.4              D-Bus-based configuration storage system
xfce4-cpugraph-plugin-1.1.0_1  Graphical representation of the CPU load
xfce4-datetime-plugin-0.8.0    Datetime panel plugin for the Xfce desktop
xfce4-desktop-4.14.3           Xfce's desktop manager
xfce4-mixer-4.11.0_5           Volume control for the Xfce desktop
xfce4-mpc-plugin-0.5.2         Musicpd client plugin for the Xfce panel
xfce4-netload-plugin-1.3.2     Network Load plugin for Xfce4
xfce4-notifyd-0.6.2_1          Visually-appealing notification daemon for Xfce
xfce4-panel-4.14.4             Xfce's panel
xfce4-pulseaudio-plugin-0.4.3  Panel plugin for controlling PulseAudio mixer
xfce4-screenshooter-plugin-1.9.7 Application and panel plugin to take screenshots
xfce4-session-4.14.2           Xfce's session manager
xfce4-settings-4.14.3_1        Xfce 4 settings application
xfce4-taskmanager-1.2.3_1      Task manager for the Xfce desktop
xfce4-terminal-0.8.9.2         Terminal emulator for the X windowing system
xfce4-timer-plugin-1.7.1       Timer plugin for Xfce
xfce4-tumbler-0.2.9_6          Thumbnail service for Xfce desktop
xfce4-verve-plugin-2.0.0       Command line plugin for the Xfce Desktop
xfce4-weather-plugin-0.10.2    Weather plugin for the Xfce panel
xfce4-wm-4.14.6_2              Xfce's window manager