Plasma Dialog used to change the item's visiblity but this is no longer the case, so it would animate when a window is shown and the source has changed in the meantime.

Changed volume, waited for OSD to disappear, changed brightness, OSD would no longer show while animating from the old pixmap.
Changed volume, and changed brightness right away, OSD would still animate

WIP because the first animation for each icon item isn't animated as the item is usually assigned a window which then becomes visible as such blocking the animation :/ Turns out this bug isn't caused or related to this at all \o/ In Desktop Containment the applet container is invisible initially so it always goes through a hide-and-show cycle