I mentioned generating an error when the menu is not a single item and when inserting at position N could break a menu in half or more, and I specifically said something for the case you're mentioning.
mIRC is generating the menu so it already know what's the exact design of the menu, it's entirely possible for mIRC to modify the order, it's just that the current design makes a lot of sense, and this suggestion, while not a bad idea in itself, doesn't make more sense if any.
I think @OP wants full control of the popups menu of his @window, which is extremely fair, and it's already a big problem when people have menu * { in their script, bloating your own popups menu.
I think to solve this much deeper issue, we need a prefix event for the menu event, which would indicate that if this scripted menu event is the first one to be used to build the popups menu for the @win, then only that popups menu would be used, guaranteeing you that either you get your popups as you want, or else it means there's another menu matching that window name, and you can get rid of it.
