What version are you playing on? r33? And what clothes are you wearing on your character?
I'm playing on windows and I was wearing the goth lolita outfit. What I noticed was with the normal scenes it would automatically unequip it for the scenes and the requip it after. for this special scene it didn't unequip the outift but still put the collar on even though you can't wear a neck slot with the goth lolita dress.