Richcombo - change the contents after init

Hi.

I have a plugin that uses the richcombo plugin. My plugin populates richcombo with some items. After the editor has loaded, a user may click on one of the links in the richcombo and get a dialog where he can select which items he wants to see in the richcombo. After closing this dialog, I want to refresh that list with clientside code. Is this possible?

The important code is:

editor.ui.addRichCombo('MyPlugin', {
                label: "Insert",
                className: 'myClassname',
                showAll: function () { buildList(this, config.MyPlugin); },
                panel:
                {
                    css: [config.contentsCss, CKEDITOR.getUrl(editor.skinPath + 'editor.css')],
                    multiSelect: false,
                    voiceLabel: lang.panelVoiceLabel
                },

                init: function () {
                    var rebuildList = CKEDITOR.tools.bind(buildList, this);
                    rebuildList(); // Initial call
                    // I bind buildList function so that that function has access to "this" later
                    $(editor).bind('rebuildList', rebuildList);
                },

                onClick: function (id) {
                    openIFrame(id, this);
                }

            });

            var buildList = function () {
                for (var i in myItems) {
                    var item =myItems[i];
                    var html = "<img src='" + item.iconSrc + "' class='' style='border: 0 none; margin-right: 4px;vertical-align:middle;' />" + item.text;
                    this.add(item.id, html, item.text);
                }
            };
            var triggerBuildList = new function(editor){ $(editor).trigger('rebuildList'); };

As you can see, buildList is incomplete (I always add items to the list, no removal is done).
However, whenever I add to the list after init has been run, I get a javascript error the next time I try to open the richcombo stating that
"n.getById(p) is null" in firefox and "SCRIPT5007: Unable to get value of the property 'removeClass': object is null or undefined" in chrome and IE9

Is this not possible to do at all? Can I work around this by deleting the old richcombo completely and creating a new one?

Thanks for any help!
ElChe