Double counting sum in chart when columns are missing

[anothergreg]

I have two datasources; an employee census file (EEID, Title, Start Date, End Date) and an activity list (EEID, Activity Description, Activity Quantity, Activity Complete Date).

I have logic that checks an activity to apply it to an employee and their title while they are employed, and sums the quantity of the activity logged.  Logic is below.

=if((((Start Date)<=(Activity Complete Date))and((End Date)>=(Activity Complete Date))),sum(Activity Quantity))

My Straight Table Chart contains information grouped by other columns available in the data (Cities, for example) and it will not work unless I include Activity Complete Date in the Chart.  If I remove it, I get multiple entries of Activity Quantity. If I have Title included (which is a 1x1 relationship with Start Date and End Date, showing a person's position in the company at a given point in time) I will have a duplicate row with the same Activity Quantity count even though the Start Date and End Date are completely outside of the Activity Complete Date.

Yet as soon as I include Activity Complete Date in the Chart, it corrects itself and I get an accurate count.  What's happening here to cause this issue?