Just put a new starter motor in my dads range rover, (p38 middle shape) so i go and start it and fires up loverly, leave it for a bit, turn it off, put tools away etc.. then start it again and the stater stays engaged with the engine running.. turn the key off and the stater is still spinning, so take the lead off the battery and it stops, put the lead back on, starter is still running

is the new starter faulty? or is there any other reason?
many thanks Matt