Despite this UI seeming very touch-centric, it was actually totally boken for the touch use due to the use of mouse-specific code, namely setting the current applet only when the mouse moved and also hiding the tooltip when the mouse edited the area--neither of which are compatible with authentic touch events when handled by a mouse area, because the synthesized mouse position exits the mousearea as soon as the finger used to touch the screen is retracted.
This is fixed by setting the current applet when clicked/touched as well, and removing the onExited signal handler to hide the tooltip, which was unnecessary anyway because the tooltip gets hidden by other things and this still works.
Now touch interaction with panel applets while in panel edit mode works as expected.
BUG: 439918 FIXED-IN: 5.22.5