I was creating a report for a customer that had provided a spreadsheet as a data source and noticed something very odd in the Field Explorer. There was only one table but the field tree had several nodes that could be collapsed and expanded, with several fields in each node. After a bit of searching I found anarticle article on the BO website that describes this behavior.  Apparently this feature was added to XI release 2. 

If you have a dash in your field names and 2 fields start with the same characters up to the dash then Crystal will put those fields under a node.  So if your fields were like this:

Address1-City
Address1-State
Address1-Zip

There would be a node called Address1 with 3 fields below it. Not sure I would have ever thought to add dashes to field names but if you start seeing nodes in your field tree you will at least know why they are there.