According to jQuery documentation http://docs.jquery.com/Utilities/jQuery.extend#deeptargetobject1objectN, the target object of the extend method should come before source objects.
However in macro-browser.js:
var selectedParams = t.selectedMacro ? $.extend(t.selectedMacro.params, {}) : {}; // make a copy
The target and the source are swapped.
It should be:
var selectedParams = t.selectedMacro ? $.extend({}, t.selectedMacro.params) : {}; // make a copy

This bug causes a problem if the macro being edited has parameters unknown to macro browser. The effect is that these parameters are not passed to the preview iframe.