SUMMARY kwin has a change in when `ConfigureNotify` is sent: https://invent.kde.org/plasma/kwin/-/commit/7b486e215d44bbd9fdeb8f1180c76fb16ec6a311 The above change conforms to ICCCM, but it breaks Java apps using Swing: after maximizing the app window, in popup menus, the app considers the mouse cursor to be at a different position than it visually is, as if the app window is in the position before maximizing. We suspect this is caused by AWT special-casing `ConfigureNotify` behavior on a WM whitelist: https://github.com/openjdk/jdk/blob/88ccbb60919e4523064b0da17184eedcd9efa087/src/java.desktop/unix/classes/sun/awt/X11/XWindowPeer.java#L772 And `kwin` is not in the list. Making `kwin` disguise as `mutter` fixes the problem, which confirms the theory. Upstream bug report: https://bugs.java.com/bugdatabase/view_bug?bug_id=JDK-8338752 STEPS TO REPRODUCE 1. Start KDE Plasma 6.2-dev. 2. Start the Java app `jdownloader2`, unmaximized. 3. Move the app window to the screen center. 4. Maximize the app window. 5. Right click to show the popup menu. OBSERVED RESULT Mouse is considered to be to the top-left of its actual position. EXPECTED RESULT Mouse works alright in the menu.
Created attachment 172838 [details] screenshot