When the user opens a submenu containing items with the style `menu::checks::option` and clicks an option, the radio button logic doesn't work. This bug was discovered and fixed by nanapro.org forum user "huycan" (I'm just submitting the PR). See this forum post: http://nanapro.org/en-us/forum/index.php?u=/topic/1256/ggleave-a-menu-open
As mentioned in more detail in the forum post linked above, my understanding of why this happens is that `menu_builder::checked` fails because the `menu_window` of the submenu is created with the `menu_builder` object used by the parent menu.