I can safely say that this bug is not present in the z15 test patch as i tried three different ways to do this, all of which failed....
1. Slide around the carpark before booting it towards one end and handbraking sideways at speed until i came to a stop in a straightish slide, then pause, add objects around the car, save layout, and then when i tried to save the SPR i got the 'replay was not being recorded' message.
2. Start off on the carpark with no layout selected, hammer around and pull the same sideways slide and save the replay, then open up the replay and fast foward to the end, add the objects and then save the new layout, when i watched it back the cones i added around the car were not there, possibly because i was racing on an empty carpark without a layout loaded when the SPR was saved,and as i had saved a layout, i wasn't in fact racing on that layout in the original replay, or so i thought, so.....
3. make a new layout called bug.SPR with 1 cone added in a random place, start the race on that layout and then do the same sideways thing again, save replay, open it and add objects, but then over-ride the existing layout so that the layout i was racing on when the SPR was recorded had the same name as the now edited one, but again, the objects around the car were not there.