According to the following steps the problem can occur：
Under Ubuntu 20.04.5, the problem can occur according to the following steps
1.run the qwindow-compositor demo that comes with Qt, in the Qt installation directory /Qt/Examples/Qt-5.15.18/wayland/qwindow-compositor/.
2. Run the program in untitled.tar.gz.
3. After the untitled program starts, click the click button to bring up a window with a red background color.
4. When you mouse over, the window will turn green, mouse click to close the window.
5. Click the click button again, the background color of the pop-up window will be green. With X11 performance inconsistent, click again should also be the default red background.