https://bugs.winehq.org/show_bug.cgi?id=49348
--- Comment #3 from Rafał Mużyło galtgendo@o2.pl --- Given that there seems to be only one place in wine where this hint is set (dlls/winex11.drv/window.c: update_net_wm_states), the question would be: what exactly is wrong with the window that owns the dialog in the case when it gets skipped ?
Perhaps that difference between _NET_WM_WINDOW_TYPE_NORMAL and _NET_WM_WINDOW_TYPE_DIALOG has a more significant meaning than the gnome-shell devs thought ? _NET_WM_STATE_SKIP_TASKBAR does exactly what it's supposed to do, but it might be that the window hierarchy in the skipping state hits some quirk that simple test in update_net_wm_states fails to account for.