Heidelberg,
Unless they have changed the Satellite that BA and VS use the passengers do need to go through security again after Immigration. I have not been through MCO in over 2 years but last time I was we had to go through it. Now I admit I am usually operating as the crew (ba) so we were always smuggled out through a back door straight onto our crew bus but the few times I did do it as a passenger it was the same rigmarole as EI as you are entering a common boarding area before boarding the train to the main terminal and the TSA have no faith in other airports security procedures!