A while ago I had decided to try cleaning my cobs because I thought it had gone sour. I used Ancient Age which is a bourbon whiskey which actually tastes pretty darn good, *fruity drinks are more to my liking then something that strong, It's a taste thing* and I cleaned the bowl and shank which made the mortise swell. After a couple days drying it still wouldn't fit so I had to sand it down a bit and now it fits like a good shoe.
so if cleaning a cob don't leave to much of whatever you're using on the pipe cleaner and if it swells then either wait till it dries completely or sand it a bit.