Ah, you've found the dark secret of the UFO's. When you put them away, like in a closet, they come to life when you go to sleep. They gang up together to wreak havoc on our minds by losing their pattern directions, getting mixed up with other projects, hiding their major block pieces, and breeding indiscriminately.. that's why they're always such a mess when you find them!
BTW, socks join in on the conspiracy!