I did say it was experimental! :-/

Fix issue when bootstrapping multiple maps, jquery's each was calling the callback with a parameter and it was attempting to use it as a settings array.

Fixed it by isolating the callback.

js/gmap.js

@@ -523,5 +523,5 @@ if (Drupal.jsEnabled) {
 }
 
 Drupal.behaviors.GMap = function (context) {
-  $('.gmap-control:not(.gmap-processed)', context).addClass('gmap-processed').each(Drupal.gmap.setup);
+  $('.gmap-control:not(.gmap-processed)', context).addClass('gmap-processed').each(function () {Drupal.gmap.setup.call(this)});
 };