Actual cost line displays after current date

Answer:

This will only happen if

1. A task has actual cost greater than zero

2. The task has no activity before the current date.  

Since there is no activity before the current date, Milestones has no choice but to allocate the funds after the current date.  Reasonably, a task which is in the future and has no progress (zero % complete should have no actual cost.  To display a graph which accurately shows $ spent before the current date, 1) Choose the Allocate to current date option for the ValueSet and 2) Be sure that tasks which are in the future have a value of zero.