CP850 doesn't support the C1 control characters, so you get the
fallback instead, which is the scheme for encoding the Meta modifier
when bit 7 isn't available. This means that Ctrl+Shift+letter
combinations can't be distinguished from Ctrl+Alt+letter, but since
Ctrl+Alt+letter combinations are suppposedly reserved for global
shortcuts in Windows, they might still come in handy occasionally.
There indeed is another scheme of encoding C1 control characters with
an ESC followed by the base character, e.g. ^[A instead of ^[^A, but
that would have made the Ctrl+Shift+letter keycode the same as
Alt+letter rather than Ctrl+Alt+letter, which is why I chose the Meta
scheme.
I hope that makes some sense.