Application Menu - Gnome Tweaks - Toggle On & Off Reverse Function. Ubuntu 18.04

I am Struggling to Understand the behavior of Application Menu in Gnome Tweaks..

when the toggle button shows its on - icon is not visible.
when the toggle button shows its off - a icon is visible on window.

is it a bug or am I wrong?

Please look at bottom right corner for the icon in below images.

The "Application menu" is a global menu for an application, that by default is displayed on the Gnome topbar for the application that is in the foreground. Gnome applications such as Files, Calendar, Software, etc. display several options there. For other applications, the menu usually contains the "quit" option only.

Turning off the application menu in Gnome Tweaks removes it from the top bar of gnome shell. By default, it will now be included as an extra icon in the top bar of applications that use client side decorations, such as the gnome applications (Files, System Monitor, ...) and others (e.g. Shotwell).

Whether and where it is available in the top bar of gnome applications or not is determined by the dconf setting org.gnome.desktop.wm.preferences button-layout. By default in Ubuntu 18.04, this is set to 'appmenu:minimize,maximize,close'. The string "appmenu" stands for the application menu. Removing that string will prevent that application menu from ever being displayed in the top bar.

In future gnome shell versions, the application menu may be removed from the Gnome top bar.