To give more details:
- The report using the DataFlex embedded database showed 125 columns in the table
- The report using ODBC (Oracle) showed 1094 columns in the table

For each column DR stores a number of characteristics such as length, precision, name, type. Depending on the length of the column name it is between 22 and NN bytes per column. The report has 969 columns extra which explains the size difference of the report definition.

Conclusion: Not a bug.