ClarisImpact automatically fills all inserted rows and columns with sample data, when you insert rows or columns into the table which is attached to a data chart. To generate the sample data, ClarisImpact simply duplicates the Row or Column that was selected just before invoking the Insert Cell command. If you replace the sample data with your data, the Chart will graph properly.
This only happens with the table which is attached to a Data Chart. It does not happen with the Table Model even though it might appear to be similar to a Data Chart.