Hmm, I don't see anything out of the ordinary on the official shortcut listing. Curiously (or not?), the Windows defaults are not listed (F10 or tap ALT to highlight the menu bar, or ALT+(menu shortcut) to open a menu), which may be something of an oversight as the compacted ("hamburger") menu I don't think works in the Windows-default way, but recreates it nonetheless (ALT+F does indeed bring up the File menu, etc., even though they're actually submenus, nice).
So yeh, I never noticed anything nonstandard about it, besides the extremely low profile design (eschewing toolbars/ribbons entirely). Unless it's differently behaved on other Windows versions, or you have, like, AHK or other shortcut/modifier thing installed, or something else paranoid like that(!?). But yeah, dunno.
Tim