Similar thing happened to me with shallots couple of weeks back. I had about 30 planted into pots to give them a start while waiting for this gosh-darned awful wet and cold weather to settle so I could plant them in the allotment. (I need to plant something soon, this is my first go at allotmenting, and I want to start planting :D )
Plastic greenhouse went walkabout - not far, but far enough. Compost and shallots all over the lawn. We repotted them, and I doubt they came to any harm.