Different variables are given the same identifier

Created by: j201

http://sweetjs.org includes the following code as an example of hygienic renaming:

macro swap {
  rule { ($a, $b) } => {
    var tmp = $a;
    $a = $b;
    $b = tmp;
  }
}

var tmp = 10;
var b = 20;

swap (tmp, b);

While different names are generated for the macro variable tmp and the global tmp in version 0.2.2 and earlier, 0.2.3 and 0.2.4 are giving me the following:

var tmp$111 = 10;
var b$112 = 20;
var tmp$111 = tmp$111;
tmp$111 = b$112;
b$112 = tmp$111;
;

The same happens in the web editor.