WHY does the cat poop in it's kennel?

Story: Got this cat from the shelter September 2010 - she was 5 or 6 months old. The first month she was kept in her kennel every night and whenever I wasn't home (she had front claws and I had / have a nice couch). After that, she was only kept in the kennel 7-8 hours when I slept. Had no problems with her and the kennel the first 5 months. Then, had two incidents (one in February, one in March) where she pooped in her kennel. Thought it might be worms or an infection but no. I was out of town for some time this May, so the cat stayed with a friend. This friend let her roam all day, almost no time spent in the kennel. No problems there. When I got the cat back and put her in the kennel at nights again (I don't want her breaking nick-nacks I have OR climbing / biting things in the kitchen, as she has done), she pooped. So I let her stay out, and when she started to paw at my bedroom door, I'd put her in her kennel, usually for 2-4 hours. This seemed to work, until she did it again, last night. I am tired and need to figure out what is wrong with this cat. Any suggestions? Not any great help via web surfing. THANK YOU!!!!