Is this planned start date and time in the future? If not then I think you are just describing standard behavior. when you go into sm37 active and finished jobs have a planned start time which you don't see when you are defining it as immediate but what's the difference if the start time is in the past? Hasn't it already started immediately?
If the planned start date and time is in the future then can you let us know how you are creating these jobs, sm36, from a selection screen via execute in background or are you creating these jobs programmatically using SUBMIT VIA JOB?