I'm using the "Shows tooltip window thumbnails" behavior when clicking a grouped task in KDE 5.22.4 on Manjaro. When clicking a task group with multiple windows, the thumbnails are in a tooltip instead of a regular menu and exhibit tooltip behavior of closing if the mouse pointer exits the tooltip area or after a timeout has expired. This is a usability problem because when using this to switch windows, one needs to be very careful with their mouse movement to avoid closing the tooltip and having to repeat the action. This is especially noticeable if the direct path to the desired window requires passing over other icons or groups in the taskbar. An unnatural L shaped mouse movement is needed to keep the tooltip open.

When the thumbnail display is the result of a click rather than a hover, it should behave like a menu instead of a tooltip. That is, the thumbnails picker should remain open until the next click regardless of mouse pointer movement or time. That way the user is able to easily correct themselves if they drift the pointer out of the menu area and to take as long as they need to inspect the available options. The behavior is then consistent with other click-to-expand menus across OSes and DEs, including KDE itself.