When creating an Ad-Hoc Query you have the ability to either click on the small "plus" sign or double click on the actual text in the Browse for fields in area. If you click on the plus sign this will cause the child fields to drop down under the primary field. If you double click on the text itself then the same child fields will drop down but will show as the same fields twice instead of only once.
This is working correctly. The design of the query is that the plus sign must be used for the drop down. When you double click on the text that adds the extra fields this is to allow more information into the query.
Steps to Duplicate
1. Go to Analyst > Information Library 2. Click on Add an Ad-Hoc query 3. Click on the query you will need, ex. Constituents 4. In the Browse for Fields in area, click on the plus sing next to any parent filed, see drop down selections > click again to close options 5. In the Browse for Fields in area, double click on the text instead of clicking the plus sign. Now observe that it doubles the fields