I had a similiar problem with my Specialized Dolce Elite with the same Shimona set up you are talking about. The chain fell off when I went from granny to second. I took it to my LBS and insisted they ride it and see what it did (I had already taken it in three times by then and I think they thought I was crazy). They finally realized it was a problem when they took it for a ride and so decided to keep my bike until it was fixed. The thing was, it wouldn't do it when they put it on the rack. You had to be riding it for the problem to occur. Any hoo - they were finally able to fix the problem. I don't know how exactly but chain hasn't fallen off lately so I'm pleased.
I should add I've only been able to ride 10 miles since it as fixed and then promptly sprained my ankle but it was working very nicely before said injury.