The detail section is rendered as many times as the number of the data records when a data source is added to the report. If the Table and the report are both bound to data (Report.DataSource is set in order to use the fields from the data source outside of the table) and the table is inside the Detail section it will be repeated (with the headers) for every row in the report's data source. For that reason, I would recommend to either remove the datasource of the report or move the table into a group header or footer (the group can be static).
I noticed that you have related question here: https://www.telerik.com/forums/row-groups-in-a-table-in-grouped-detail-section
. Please review my answer and let me know if you have any further questions.
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