Because you are using table calculation.
Under table calculation, you can not get right g.total in most of the case.
Without seeing your data , we cannot provide the solution.
Please attach packaged workbook.
This is one of Tableau's trickiness.
When you use table calc, grand total's behavior becomes very strange.
Here is a work around though.
Duplicate data source with Union.
You get "Table Name"
Woah that is a lot of work to sum something... It works, just insanely painful to do! Thanks for your help.
That's absolutely reasonable feeling.
Table-like view is not Tableau's powerful arena, where excel lover typically want.....