[Solved] Excel is correcting a formula that isn't brok

A1: Calls In
B1: Calls Out
C1: Faxes
D1: Hours Worked
E1: Total Contacts

E2: =SUM(A2:C2)

When I enter a value in A2, sum shows that value.
When I enter a value in B2, sum adds it in.
When I enter a value in C2, sum adds it to the total.

When I enter a value in D2, the SUM formula changes to =SUM(A2:D2).

Arrrrrrrrgh!!!!! Why is this happening!!!!!

Cool! What other impacts does this have? Are there other features that will be disabled?