%1 is unquoted by definition and has to remain so for compatibility with Explorer.
The new version we just released has a change so that dragging programs to toolbars adds {filepath} as their argument instead of %1, so paths which need quotes will now get them with these buttons.
(Existing buttons are unaffected, so you may still need to edit them and either add quotes around the %1 or change the %1 to {filepath}.)