MouseUp (without initial MouseDown) on the "Mute/Unmute Toggle Button" toggles mute state, but shouldn't
xfce4-pulseaudio-plugin version: 0.4.1 (Debian Stable/Buster with Xfce DE). I didn't test on latest version because I'm lazy :-P
Reproduce: If you click MouseDown and drag on the Volume Slider and max out your audio and your mouse pointer goes to the right off of the volume bar such that when you release MouseUp your pointer is now above the "Mute/Unmute Toggle Button", you trigger the toggle action and your volume becomes muted (or unmuted if it was already muted)..... when all you were really trying to do is turn up your volume to maximum.
Solution: The "Mute/Unmute Toggle Button" should only respond to a full MouseClick (MouseDown followed by MouseUp) and not just a MouseUp event.
Thanks for a great minimalist DE (and pls keep it minimal)