Ah, I didn't intend to actually change behavior. Feel free to revert http://github.com/nex3/arc/commit/cbf2bd3e08 (or I'll do it this evening -- and figure out what I'm missing).
edit: Done (http://github.com/nex3/arc/commit/f72acc2997). I'm still unclear on why the macro form is different, and why it works in some macro situations but not others (I've added two examples to that commit)