Is there a chance you could repeat the whole route? I've got report of this bug before by one person, but I couldn't make it happen when I was trying to do it. So I'm not really sure in what situation it occurs.
Hey! Maybe you figured out what situation created the bug, but if not, I found out why. When you wait or get on your knees, if the amount of times you click grope + sniff is greater than 4, there is no dialogue choice after you take down his underwear. But if the amount of times is equal to four, there is the arrow where he "take control" after you click on it. (so I think you just need to change your "==4" to a ">=4" in the code where this event appear(hope I don't say anything stupid, since I don't know how vn's are coded ^^'))