Grand Total í Matrix report is not adding up

Hi folks!

I have this report:
Type: Matrix Report
Modules: Opportunities, Opportunities > Assigned to User
Display Columns: <empty - none>
Group By: User Name, Probability (%)
Teams: Global (Primary)
Summary Columns: User Name, Probability (%), SUM: Amount
My problem: The Grand Total is not tallying up when there are more than 1 number per column:

What could I be doing wrong?

Takk,
KGM