Oh my....boy do I have the same problem! I will tell you the story of what happened with me, long but I think it will be useful to you.
When it started getting cold, we brought out the down comforter.
One night I noticed Pyjamas dashed out into the bedroom in front of me, jumped on the bed, scratched around and took a dump!( only way to describe that massive poo, sorry! LOL). I was so shocked!
I washed the comforter as recommended...put it back on the bed thinking it was a freak accident. But a few nights later during the nite I awoke to a horrifying stench to find he had done it again ><!
Washed the comforter. again. and those things STINK when they are washed...the smell of wet feathers...blegh.
So we put him in the bathroom at nite because he couldn't be trusted and we had nothing to replace the comforter with.
One day while playing in the cat tunnel with Ruby, he scratched around inside and had a massive poo inside of it. Oh my goodness...what a nightmare! Luckily it was plastic so easy to clean and neutralize, but still a pain. Then I wasn't sure if I could trust him around the tunnel to play in
One morning after letting him out of the bathroom, I found that he pooed on the bathmat. LOL. Washed that bathmat, put a new clean one down....eventually he pooed on that one as well but this time managed to pull the corners of it up to cover his business. LOL
At this point he's still in the bathroom at nite but we have been trying to teach him that the only place he can poo and pee is his litter box. We knew the cleanliness of the box wasn't an issue because he scratched the bed the very day I did a full clean and bleaching of all three trays.
In the bathroom, what I did was I began to move his food/water dishes onto the bath mat. cats will not eliminate that close to their food. so that stopped him. After about a week of this, I took his food bowl off and sprinkled a bit of kibble on the bathmat. I found that he would eat all the kibble off the mat (LOL such a fat boy...) but still not poo on it. after a week or so of that, I left the bathmat as is. It's been at least a month now since and he hasn't pooed on the bathmat at all since then. I think that he is actually learning.
Each time he uses the box, we praise him first and foremost before cleaning any poopy paws/butt. so he associates using the box with something good. Treats would also be helpful but he doesn't like treats all that much.
I have now begun leaving the bedroom door open during the day and testing him. Sometimes when I observe him I do catch him scratching the comforter as if he';s going to poo on it. When this happens, just pick him up calmly and put him in a litter box. After several times of taking him to his box, when he would scratch I began to squirt him with a water bottle. So he associates scratching the bed with a bad consequence.
After several times of that, now I just say, "no" when he scratches. Because he is learning what "no" means due to disciplining him in other areas of the house, he will usually stop, jump down, and go to his box.
Now we leave the bedroom door open at nite as well to test him further. So far we have had no accidents. When he has diarrhea I do shut it if I can't keep an eye on him because I don't want him to regress because of a bad tummy. So you can shut the door when you feel it may be necessary. In the beginning, when you feel safe enough to keep the door open for any amount of time, you'll need to keep an eye on him because he will learn ONLY when you change his behaviour. So he will only really learn if you catch him about to do it and take him to his box, this is the prime moment to teach him.
Another thing you can try is what I did with the food bowls on the bathmat. Maybe get a different crappy comforter cover to use during the day, put his biscuit bowl on the bed and see what he does. He may decide that he doesn't want to poo there when his food is there. then during the day you can sprinkle some kibble on the comforter and see what happens. Maybe he'll get the message.
We are at the point now where we are ready to let him sleep with us again (but haven't yet due to other reasons, namely Ruby), so I feel like this is a big accomplishment and am very proud of our patience with him. I know it is frustrating beyond, but there is hope. Raggies are very smart and you CAN teach them what are desirable behaviours and which aren't.
I wish you the best of luck. Think up a plan that will be appropriate for you, and stick to it and be patient! I have faith that both of our sweeties will learn to stop.