https://bugs.winehq.org/show_bug.cgi?id=45899
--- Comment #23 from Konrad Materka kmaterka@wp.pl --- I checked how it works on XFCE: mask is working as expected, both plain wine and staging. When I click on the transparent area clicks do nothing. It is not how MS Windows works, but this should not be a problem for end users.
I'm not a KDE developer nor I have any decision power, I just try to fix it on KDE side. In my opinion this is an issue on KDE side, unfortunately. Xembed is deprecated in KDE, current implementation of xembed tray icons is just a workaround or hack. It is just a proxy between SNI and xembed, on SNI click event KDE sends click events always in the top-left corner (0,0) of the icon. It is not possible to get information where the icon is rendered nor exact coordinates of the click relative to the tray icon. There is no easy fix, I tried several things and all of them break compatibility with native apps.
Off topic: do you know how to disable window mask using XCB? Is it even possible after the X window is created?