Crosstab Grand Total appears to be incorrect

Suppose you have a crosstab with multiple groups.  If you add the group totals by hand, you might find the Grand Total has a different value.

Most likely you are using distinct count for these groups.   The explanation for the discrepancy is as follows.

In group A: if you have values A, B, B, C, D, then the value for distinct count for group A will be 4.
In Group B: if you have values A, A, E, E, F then the value for distinct count for group B will be 3

However, the grand total distinct count value will be 6 and not 7 because there are only 6 distinct values in the whole column (group A and B): A, B, C, D, E, F. Returning 7 (4 + 3) would be incorrect.