Hi, to again clarify what exactly do you mean when you say "...by your own confirmation"? Is that me when I literally start the engine or is there another trigger somewhere?
At the end of pushback, you are being asked to confirm if engines started, with a text message, and GSX will wait for your confirmation. This is done by opening the GSX menu again, which at that point will show a menu with various options, like confirming the engine start or ignore it.
So GSX won't automatically detect the engines to be running, it will always you who are supposed to confirm it.
Note that, NONE of this will be seen, if you close the GSX menu from the toolbar, the manual explains that, when you are using GSX, you should never close the GSX menu from the Toolbar, because doing this will result in missing any text message coming from GSX or any eventual pop-up menu that might be required. This is general is valid in all cases when a GSX procedure is not exhausted by choosing a menu option and will continue later with some messages waiting for something or menus pop-up, for example during refueling, in the time between the truck is called and it arrives, when GSX might need to ask about the fuel quantity, or deicing in the time between deicing is called and the menu asking for choices about deicing options is supposed to pop-up, or pushback, both in the time between pushback is called and a menu with a direction is opened, or before the engine start confirmation, the message about waiting for it will be missed is the menu has been closed from the Toolbar.
That's why, as the manual suggests on Page 74, where the menu is explained, you should open the GSX menu from the toolbar only when first calling GSX, then always use the hotkey or the "x" icon to close it, and eventually close it from the toolbar only when you are done with it, usually after takeoff, even if closing is not strictly necessary.