Conditions When Hidden Fields are Included by Default
Under certain conditions, when a field is dragged into a report template and then configured for a specific action, another hidden field will also appear in the list. This hidden field is mandatory and cannot be removed, as the system knows that it is required for the operation that you are configuring. These hidden fields are included to mitigate performance issues.
Example: If a report template is based on the summary status description field and you want to configure a drilldown in this report, the report will perform much better if the summary status was added as a hidden field. Automatic addition of a hidden field is performed in situations when the report meaning will not change.