TCustomDataSetValuesList uses DataSetPrepared internally to keep track of whether it has initialized the dataset for its own use. When the WebSnap application reads the DataSet property, TCustomDataSetValuesList checks DataSetPrepared, and if the dataset has not been prepared, it sets up the dataset for use and changes DataSetPrepared to true. When the Web module that contains this values list is deactivated, DataSetPrepared changes back to false. 

DataSetPrepared is true if the dataset has been prepared (that is, if TDataSetValuesList has generated an OnPrepareDataSet event). DataSetPrepared is false if the dataset needs to be prepared before the values list can use it. 

DataSet 

OnPrepareDataSet