/event/billing/product/fee/purchase start_t not set to purchase_start_t

In a BRM 7.5 environment, when I perform a backdated purchase of a product, the purchase fee event's start_t correctly reflects the backdated purhase_start_t supplied on the deal purchase.  But in a 7.3 BRM environment, the purchase fee event's start_t is the current time.  There is nothing on the purchase fee event that reflects the purchase_start_t specified on the deal purchase.  Anyone know if there is a bug in 7.3 or if there is some configuration that would cause 7.3 and 7.5 to work differently?  I need to get to the purchase_start_t but because the product is a purchase fee