The reddit keymaps is defined as a child of the normal buffer keymap:
define_keymap("reddit_keymap", $parent = content_buffer_normal_keymap);
and shows up at the top of C-h b, can keymaps which are childs of the
normal _keymap be said to unambiguously refer to page-mode maps and if
so maybe only that keymap can be displayed at C-h m?