Why does {..} expansion using 'bindkey' quoting, but {,} and BRACE_CCL don't quote at all?

[Marlon Richert <marlon.richert@xxxxxxxxx>]

For example:

% print -r -- ${(q+):-{$'\C-['..$'\C-]'}}
'^[' '^\' '^]'
% print -r -- ${(q+):-{$'\C-[',$'\C-]'}}
$'\C-[' $'\C-]'
% setopt braceccl
% print -r -- ${(q+):-{$'\C-['-$'\C-]'}}
$'\C-[' $'\C-\' $'\C-]'
%

Is there a reason for this inconsistency? Why not always produce
quoted or unquoted output?

Also, why bindkey-style quoting? Wouldn't ${(q+)}-style quoting be
more convenient, since it's more straightforward to "unquote"?