I wonder if during one of these sex scenes they've been tempted to 'accidental' slip it in.
Me thinks said individual would be marched off set, into the awaiting police car and then been subject to repeated accidental 'slips' whilst in the showers at HM's pleasure..
Professionally you're not there to have sex.. most of the partners wouldn't be happy with you either. There's probably loads of ways.. blankets in the right spot to hide the undies.. flesh coloured pants.. and if you do get full nude then usually they're taught to 'ride' without contact.. nothing like catching an STD because you johnson got into the damp zone.. If you do get a hard on you can point it away..
What would be disconcerting is if she reached down as part of the planned scene but made for some penetration that wasn't scripted etc even when your attempting to be the perfect professional..
Sort of breaks the trust to be honest..