Volume jumps lower when dragging slider

When dragging the volume slider, as soon as I move the mouse by one pixel after mousedown, the volume slider jumps to the left.

The exact behavior varies by GTK theme.

• In XUbuntu's default Greybird theme, I do not see the issue.

• In GTK's default Adwaita theme, I see the issue, but it is subtle and only happens when clicking certain portions of the slider handle and/or not always.

• In Devuan's default Clearlooks-Phenix-Sapphire them, there is a consistent jump of about 5% volume.

• In the DarkCold theme found in the Debian repos, the slider can actually jump twice and get significantly out-of-sync with the mouse.

• The issue is visible in a large number of GTK3 themes that I have tested.

• This issue does not occur on the default sliders in awf-gtk3.

• This issue occurs regardless of whether the slider is moved immediately or long-pressed and then moved

  (Note: A one-second mousedown on the slider triggers a precision-control mode where the slider moves less rapidly than the mouse and by a maximum of 20% no matter how far the mouse is moved. If anyone triggers this by mistake, it will feel like the slider is broken regardless, but anyone using this deliberately will especially not want the slider to jump around.)

tested version: xfce4-pulseaudio-plugin 0.5.1 compiled locally

tested operating system: Devuan Excalibur (Debian Trixie equivalent) with development versions of many Xfce components