Unusual consist

I saw an unusual CSX manifest earlier this week moving north through Florence, SC. It had a single locomotive on the front and another single DPU locomotive halfway through the consist. The CSX Florence subdivision is mostly flat (the low country of SC) and most of the trains I see have two locomotives up front. It was the old Atlantic Coast Line mainline from Tampa, FL., to Richmond, VA., and still hosts three daily Amtrak trains each way.
Have others seen this sort of experimentation with mid-train DPU's?
Harry
Have others seen this sort of experimentation with mid-train DPU's?
Harry