collections with custom fields can fail to open in some circumstances

As reported at http://forums.gcstar.org/viewtopic.php?id=1151, in some circumstances collections with custom fields stop loading. This is caused by a change to the grouping lines in the gcs file. Instead of a correct section like
  <groups>
    <group id="User fields" label="User fields" />
  </groups>

the section is being replaced by
  <groups>
    <group displayed="User fields" id="User" label="PanelUser" />
  </groups>

causing gcstar to crash when trying to load the collection.