IMHO, task costs are not showing when PAYMENT is made, they show when
the liability is posted into the project budget. How does your 50/50
rule function when you pay 50% of 100 man-hours at the start, work 50
hours, and find that you are going to need 200 hours more to finish for
a total actual cost of 250 man-hours. The primary purpose of the cost
data is to provide budget estimates, cash flow requirement projections,
and monitor project progress metrics - it is not a client time and
billing application nor a accounts payable and receivables or revenue
tracking. It doesn't deal at all with when costs are paid, only when
the work that they're buying is required to be accomplished.