If you choose AU4 track in HL mode (or if it was chosen before), race lenght will be set to 1 lap instead of a practise, and it won't be changed if you'll change the track. Re-entering HL helps, but I think this lil' thing should be fixed anyway
Well the drag strip can only be 1 lap (start --> checkpoint --> finish)
You can't have a rolling start in a drag race, so you can't restart the lap by driving back to the start...