Based on the recommendation of the Rock Your Groups Guide ("Rock comes preconfigured with a general group viewer People > Group Viewer, but you can add more. Say, for instance, your church has a strong small group ministry. You may want to create a new Group Viewer page just for this ministry. You can do this by adding a new page under People (or any other page you like) and add the group viewer blocks to the page"), I've created some pages with the group viewer blocks to show only a certain group type.  Here's an example:

However, when I select an actual group, the group tree block only shows the spinning arrows.  This only happens when the ExpandedIds parameter is in the URL. Example:

I can't figure out when my configuration is wrong, or if there is a bug somewhere.  The Group tree block works just fine on the included Group Viewer page. 

Thanks!