Oh my. I feel for you. I've got a 2 1/2 yo male and he does the same thing only he sits in front of me and cries so I let him out. But I'm still seeing those yellow carpet marks on the corners of my wall. He knows he is supposed to go out. I have a female yorkie that is completely potty trained and she would die before she messed in the house. And he goes out with her and does his business. He does every once in a while go on the "paper" pee pad. And when I see a "tootsy roll" on the paper we have a big ole time. He's so proud when he see's how happy I am. But the next time I'll see a "tootsie roll" and I ask him in a disappointed voice "Why is there a tootsie roll on the floor he gets sad and goes to hide under the bed. So here is my analogy on the situation. Could it be that they are just like young children and get so busy doing what ever that they wait till the last second to take off for outside and just don't make it? I just don't understand why they do good one second and bad the next.
The only advice I can give you is for you to get a "belly band". I use one on my boy and I stick a feminine pad to it and wrap it around his belly covering his penis it is about 4 inches wide and velcros closed on top of is back. I can send you a picture of him wearing one and if you think it would work for your baby I can give you the ladies email that made mine. there like $15 if I remember correctly. Saves your carpet for sure.
Kim