The taskbar buttons are not synchronized with the actual active windows.

[tabris17]

Bug Reproduction Steps:

1. run "notepad.exe" (or other applications)
2. apply the following code to the Notepad window:

   SetWindowPos(hwndNotepad, HWND_BOTTOM, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_NOACTIVATE);
   SetWindowLongPtr(hwndNotepad, GWL_EXSTYLE, notepadExStyle | WS_EX_NOACTIVATE);
   

   At this moment, the Notepad button disappears from the Windows taskbar but remains in the CairoShell taskbar.
3. close notepad

Finally, the Notepad button still remains in the CairoShell taskbar, but the Notepad process has already terminated.