I would say it depends on whether or not the bun is still connected on one side. I base this on nothing other than the fact that to me it feels correct.

Hero/hoagie/submarine sandwiches aren't sandwiches?

Nope, not unless you cut all the way through. It's not a sandwich unless the filling is between two pieces of bread.

White City Shopping Center, L.P. v. PR Restaurants only made it to Massachusetts Superiour Court, so precident is limited, but it lets us know that a buritto is not a sandwich.

Not from the US but similar: http://www.timcrane.com/jaffa-cakes.html