When calling:

confluence.saveMacro({a:'a'}, "The body");

I see an ajax request going to:
/confluence/rest/tinymce/1/macro/placeholder
with the macro contents i just saved.

However, when the page is displayed the macro.body url parameters are empty.

In reference to:
https://groups.google.com/forum/#!topic/atlassian-connect-dev/dJM5wrmtnKo